Hot Chocolate Mug Cake

3.50 from 2 votes

This hot chocolate mug cake is rich, gooey, and ready in just 5 minutes - with a jumbo marshmallow hidden in the center that melts into a lava-style middle! It's made with hot cocoa mix, chocolate chips, and marshmallows for the perfect quick treat.

hot chocolate mug cake, covered in marshmallows and chocolate syrup, with a spoon.

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If you love hot chocolate and lava cake, this hot chocolate mug cake is the best of both worlds.

This single-serve mug cake is made with hot cocoa mix and finished with a jumbo marshmallow hidden in the center, which melts as it cooks to create a gooey, lava-style middle. When you dig in, warm chocolate cake gives way to a molten marshmallow core - just like a restaurant-style lava cake, but ready in under 5 minutes.

No eggs, no oven, and no complicated steps - just a mug, a minute in the microwave, and an ultra-indulgent dessert that's perfect for a winter sweet treat!

Why You'll Love This Recipe

A true lava-style center. The jumbo marshmallow melts into the middle of the cake, creating a soft, gooey core that mimics classic chocolate lava cake.
Hot cocoa flavor - not just chocolate cake. I use hot cocoa mix to give this cake a sweeter, creamier flavor that tastes exactly like your favorite cup of hot chocolate.
Rich and fudgy (not spongy). Skipping eggs keeps the texture dense and molten instead of cakey.
Ready in minutes. Perfect for late-night cravings or instant dessert!
Super easy to customize. Swap in flavored marshmallows, add chocolate syrup on top, or pair with ice cream for an extra-decadent finish.

Ingredient Notes

1 packet hot cocoa / hot chocolate mix: This equals about ¼ cup if you're scooping from a larger container.
- Important: This is not plain cocoa powder. Hot cocoa mix already contains sugar and milk powder, which are essential for the correct sweetness and creamy texture in this mug cake. If you only use cocoa powder, the cake will turn out bitter and dry unless you adjust it.
¼ cup all-purpose flour: Standard all-purpose flour works best here and keeps the cake sturdy enough to hold a molten center without collapsing.
¼ cup milk: Whole milk gives the richest, smoothest result, but 2% or even non-dairy milks like almond or oat milk will also work. The milk helps activate the cocoa mix and keeps the cake moist.
2 tablespoons vegetable oil: Any neutral fat works - melted butter, canola oil, or coconut oil are all fine - but vegetable oil keeps the texture extra soft and fudgy instead of crumbly.
2 tablespoons milk chocolate chips: These melt into the batter to create pockets of gooey chocolate throughout the cake. If you prefer a deeper chocolate flavor, semi-sweet chocolate chips work great too.
1 jumbo marshmallow (for the lava center): This is the secret to the molten middle. Press one jumbo marshmallow into the center of the batter before microwaving. As the cake cooks, it melts into a soft, gooey core that mimics a chocolate lava cake - no extra chocolate or fillings required!
Mini marshmallows (for the top): A few sprinkled on top gives that classic hot chocolate look and adds extra gooey sweetness as they soften and melt.

Additions & Variations

This hot cocoa mug cake is so yummy as written, but it's also easy to customize - especially if you want to play up that lava cake middle!

Extra-Gooey Lava Center

Double marshmallow lava: Press two jumbo marshmallows into the center instead of one for an even bigger molten core.
Chocolate lava upgrade: Add a chocolate square or truffle alongside the jumbo marshmallow for a chocolate-marshmallow center.
Marshmallow fluff option: Swirl 1 tablespoon marshmallow fluff into the center if you don't have jumbo marshmallows on hand.

Hot Chocolate Flavor Twists

Peppermint hot chocolate: Add ⅛ teaspoon peppermint extract to the batter and top with crushed candy canes.
Mexican hot chocolate: Stir in a pinch of cinnamon and a tiny pinch of cayenne.
Salted caramel hot chocolate: Drizzle caramel sauce on top after cooking and finish with a light sprinkle of sea salt.
Mocha hot chocolate: Replace 1 tablespoon of the milk with strong brewed coffee or espresso.

Texture Adjustments

More cake-like: Add ½ teaspoon baking powder for a slightly lighter, fluffier mug cake.
More molten: Start microwaving at 45-50 seconds and add time only if needed to keep the center soft and gooey.

Toppings & Serving Ideas

Chocolate syrup or hot fudge
Whipped cream or vanilla ice cream
Extra mini marshmallows (torched if you're feeling fancy!)
Chocolate shavings or cocoa powder dusting

☕️ Try more mug cake recipes, like this birthday cake mug cake or my easy cake mix mug cake!

How to Make Hot Chocolate Mug Cake

stirring chocolate cake batter in a mug.

pressing a jumbo marshmallow into the center of the hot cocoa mug cake batter.

marshmallows on top of hot chocolate cake batter in the mug.

Mix the batter. In a microwave-safe 12-14 oz mug, whisk together 1 packet hot cocoa mix and ¼ cup flour until combined. Add ¼ cup milk and 2 tablespoons vegetable oil, stirring until the batter is smooth with no dry pockets.
- Tip: The batter should fill no more than halfway up the mug to prevent overflow.
Add the lava center. Gently fold in 2 tablespoons chocolate chips. Press 1 jumbo marshmallow straight down into the center of the batter until it's just covered. Sprinkle a small handful of mini marshmallows on top, but do not stir - this keeps the center molten.
Microwave until just set. Microwave for 50-60 seconds, stopping when the top looks set but the center is still soft.
Rest and serve. Let the mug cake sit for 1-2 minutes before eating. This allows the cake to finish setting while keeping the marshmallow center warm, gooey, and lava-like.

Microwave Wattage & Cook Time

Microwaves are going to vary, so cook time can depend on wattage. The goal is a set top with a molten center.

1200 watts: Start at 45-50 seconds
1000-1100 watts: 55-60 seconds (perfect range for a lava center)
800-900 watts: 65-75 seconds

If the top looks set but the center is still gooey, it's done. If needed, add time in 10-15 second increments - overcooking will dry out the cake and melt away the lava center.

Step-by-Step Recipe Video

How to Serve & Store

SERVING: I like to wait a minute or two before enjoying my dessert; it can be a little too hot as soon as it comes out of the microwave.

Feel free to add more mini marshmallows, chocolate chips, or chocolate syrup to the top of your mug cake before serving. It's also great with whipped cream, chocolate shavings, or ice cream!

I'd enjoy this within 30-40 minutes of making it.

STORAGE: I don't recommend saving leftovers. They tend to get kind of rubbery and dry after 30-40 minutes. Just toss them and make a fresh cake next time you need a chocolate fix.

hot cocoa mug cake, covered in marshmallows and chocolate syrup, with a spoon.

Leslie's Helpful Tips & Tricks

Use the right mug size. Choose a microwave-safe 12-14 oz mug. The batter should fill no more than halfway up the mug - anything more and it's likely to overflow as it cooks.
Place the mug off-center in the microwave. Setting the mug toward the outside edge of the turntable helps it cook more evenly and prevents overcooked edges with an undercooked center.
Don't over-mix the batter. Stir just until smooth. Over-mixing can make the cake dense and cause the marshmallow center to disappear into the batter instead of staying molten.
Press the jumbo marshmallow straight down. Push it into the center of the batter until just covered. If it's too close to the top, it will fully melt away instead of creating a gooey lava center.
Microwave one mug cake at a time. Even if your microwave is large, cooking multiple mugs at once leads to uneven heating and inconsistent texture.
Stop when the top looks set. The cake should look cooked on top but still feel soft in the center. Overcooking is the #1 reason mug cakes turn rubbery and lose their lava center.

FAQs & Troubleshooting

I leave eggs out on purpose to create a cake with a denser, richer texture. Plus, you don't have to worry about undercooking eggs if they're not there!

A rubbery mug cake is usually the result of an overcooked mug cake. My microwave (about 1100 watts) cooks a mug cake perfectly at about 60 seconds. If you microwave is more powerful, you might need to take 10-15 seconds off the cooking time.

I recommend microwaving for at least 45 seconds to ensure the ingredients - especially the flour - are fully cooked. A little bit of liquid batter is fine, as long as it's pretty warm after cooking.

This usually happens if the marshmallow is too close to the top or the cake is overcooked. For a gooey lava center, press the jumbo marshmallow fully into the center of the batter so it's just covered, then microwave only until the top is set. Overcooking will cause the marshmallow to fully melt and disappear instead of staying molten.

Mini marshmallows work best as a topping, not for the center. They melt too quickly and don't create the same lava effect. For a true molten center, a single jumbo marshmallow works best. If you don't have one, marshmallow fluff or a chocolate square are better substitutes.

Yes, but you'll need to adjust the recipe. Hot chocolate mix already contains sugar and milk powder, which this recipe relies on. If using cocoa powder, add 2 tablespoons sugar and use milk instead of water to avoid a bitter or dry cake.

More Chocolatey Mug Cakes

I hope you love this hot cocoa mug cake! If you give it a try, I'd love to hear what you think - make sure to leave a comment 💭 and review ⭐️ below!