The boiling water makes this cake batter look thinner than most cake batters, and that can be a little alarming the first time you whisk it in. Don’t reach for extra flour. That loose batter is what bakes into a tender, moist chocolate cake, and it pours easily into a 9×13-inch pan if you take your time.
I like the contrast here: a soft cocoa cake underneath a smooth semisweet chocolate topping, with peppermint extract and crushed candies giving the finish its cool, crisp bite. The cake needs to cool completely before the topping goes on, so the ganache settles into an even layer instead of sliding across a warm surface. Once it sets, each square has a fudgy top and a tender crumb beneath.
Kitchen Note
Don’t pour the topping over a cake that’s still warm. I wait until the pan and cake feel completely cool, then the chocolate stays in a neat, even layer instead of turning runny at the edges.
Save this Peppermint Fudge Cake for its tender chocolate crumb, smooth fudge topping, and crisp peppermint finish.
Why This Chocolate Cake Batter Should Look Almost Too Thin
Once the boiling water goes in, the batter loosens dramatically. That’s expected. The cocoa absorbs hot liquid as the cake bakes, and the thin mixture spreads into the pan without needing to be pressed or smoothed into place. Adding flour to make it look more like a thick butter cake batter changes the balance and can leave the crumb heavy.
The other useful detail is that the cocoa goes into the dry ingredients before any liquid. Whisking it with the flour and sugar breaks up clumps and distributes it through the batter, so you don’t end up with pale streaks or little pockets of cocoa. After the wet mixture is added, whisk just until smooth; then pour in the boiling water slowly. The final batter should flow freely from the whisk. Handle the bowl carefully as you pour, because that thin texture can splash more easily than a thick batter.
What Gives This Cake Its Tender Crumb and Peppermint Fudge Finish
- Unsweetened cocoa powder — This gives the cake its chocolate flavor without adding sugar. Break up any compacted lumps as you whisk the dry ingredients; clumps are much harder to work out once the liquids are in.
- Buttermilk and baking soda — Buttermilk brings tang and moisture, while its acidity works with the baking soda to help the cake rise. Regular milk doesn’t provide the same acidity, so I wouldn’t swap it in without changing the leavening balance.
- Neutral oil — Oil keeps the crumb soft without adding a distinct flavor that competes with the cocoa and peppermint. Use an oil with a mild taste rather than one that would announce itself in the finished cake.
- Semisweet chocolate chips and heavy cream — Together they make the smooth, pourable fudge topping. Semisweet chocolate keeps the finish from becoming overly sweet; the heavy cream gives the melted chocolate a soft, spreadable texture.
- Peppermint extract and crushed peppermint candies — The extract flavors the chocolate itself, while the candies add a brighter peppermint note and a crunchy top. Peppermint extract is concentrated, so measure it carefully rather than pouring straight from the bottle.
Mixing, Baking, and Topping the Cake Without Guesswork
Whisk the dry and wet mixtures separately
Start with the oven at 350°F and grease a 9×13-inch baking pan. Whisk the flour, sugar, cocoa powder, baking powder, baking soda, and salt in a large bowl until the cocoa looks evenly distributed. In a medium bowl, whisk the eggs, buttermilk, oil, and vanilla until combined. Pour the wet mixture into the dry ingredients and whisk until smooth, scraping the bottom of the bowl so no dry pockets remain.
Pour in the boiling water slowly
Whisk in the boiling water a little at a time. The batter will become thin, and that’s the right texture for this cake; don’t try to thicken it. Pour it carefully into the greased pan, keeping the bowl close to the pan to avoid splashing. A quick look across the surface should show an even pool of batter with no dry streaks.
Bake until the center gives a moist-crumb test
Bake for 30–35 minutes. Check the center with a toothpick: it should come out with a few moist crumbs, not wet batter and not completely dry. If it’s coated with liquid batter, give the cake more time and check again. Set the pan on a wire rack and let the cake cool completely, about 1 1/2–2 hours.
Make a smooth topping and let it set
Put the chocolate chips in a heatproof bowl. Heat the heavy cream in a small saucepan over medium-low for 3–5 minutes, until it’s steaming and small bubbles appear at the edge; don’t let it boil. Pour the cream over the chocolate and leave it undisturbed for 5 minutes, then stir until smooth and mix in the peppermint extract. Pour the topping over the cooled cake, spread it evenly, sprinkle on the crushed peppermint candies, and let it set for 30 minutes before serving.
Two Ways to Adjust the Peppermint Finish
A smoother chocolate top
Leave off the crushed peppermint candies and keep the peppermint extract in the topping. The cake still has a clear peppermint note, but the surface stays smooth and the chocolate flavor comes through more directly.
A gentler peppermint flavor
Omit the peppermint extract and keep the crushed peppermint candies on top. The candy gives each slice a milder minty finish, with the semisweet chocolate taking the lead.
Storage and Reheating
- Refrigerator: Store covered for up to 4 days. The cake stays moist, though the peppermint candy topping gradually softens.
- Freezer: Freeze individual slices in an airtight container for up to 2 months. The cake and topping freeze, but the candy may lose its crisp texture as it thaws.
- Reheating: Reheating isn’t needed for this cake. Let a slice lose its refrigerator chill before serving; microwaving can soften the fudge topping and make the candy sticky.
Questions That Come Up With Peppermint Fudge Cake
Peppermint Fudge Cake
Ingredients
Equipment
Method
- Preheat the oven to 350°F.
- Grease a 9x13-inch baking pan.
- Whisk the flour, sugar, cocoa powder, baking powder, baking soda, and salt together in a large bowl.
- In a medium bowl, whisk the eggs, buttermilk, oil, and vanilla extract.
- Whisk the egg mixture into the dry ingredients until smooth.
- Slowly whisk in the boiling water.
- Pour the thin batter carefully into the prepared pan.
- Bake for 30–35 minutes, until a toothpick inserted in the center comes out with a few moist crumbs.
- Cool the cake completely in the pan on a wire rack, about 1 1/2–2 hours.
- Put the chocolate chips in a heatproof bowl.
- Heat the heavy cream in a small saucepan over medium-low heat for 3–5 minutes, until steaming with small bubbles at the edge.
- Pour the hot cream over the chocolate and let stand for 5 minutes.
- Stir the chocolate and cream until smooth.
- Stir in the peppermint extract.
- Pour the topping over the cooled cake.
- Spread the topping evenly.
- Sprinkle with the crushed peppermint candies.
- Let the topping set for 30 minutes before serving.
