This small birthday cake is a classic small batch yellow cake recipe layered with flavorful filling and frosting. The 6-inch layer cake showcases vanilla flavor, a perfectly tender crumb, and makes the perfect base cake recipe. Chocolate swiss meringue butterceam frosting and strawberry cream filling combine with the vanilla cake in this deliciously sweet birthday cake!
Make the filling first. In a small microwave-safe prep bowl, sprinkle the gelatin over the water. Let the gelatin bloom for about 5 minutes.
1 ½ teaspoons water, 1/2 teaspoon unflavored gelatin powder
While the gelatin is blooming, puree the strawberries with the maple syrup in a blender or food processor. Transfer to a small bowl.
1/4 cup fresh strawberries, 1 tablespoon pure maple syrup
Once the gelatin has bloomed, microwave for only a few seconds to liquify the gelatin. This should only take 3 to 5 seconds. Do not overheat. Whisk the gelatin liquid into the strawberry puree. Set aside.
In another small bowl, whip the heavy whipping cream to stiff peaks. Fold the strawberry puree into the whipping cream until thoroughly combined. At this point, you can sweeten the strawberry filling to taste - keeping in mind the cake and frosting are sweet. Cover the bowl with plastic wrap and refrigerate until ready to assemble the cake.
1/4 cup heavy cream
Cake
Preheat the oven to 350F degrees and adjust the oven rack to the middle position. Line the bottom of 2 6-Inch round cake pans with a piece of parchment paper cut to fit. Lightly grease the pans.
In a small mixing bowl, whisk together the flour, baking powder, baking soda, and salt.
In a liquid measuring cup, measure out the milk and stir in the sour cream.
1/2 cup milk, room temperature, 1/3 cup full fat sour cream, room temperature
In a medium mixing bowl, add the sugar and oil. Mix until smooth. Add the egg and vanilla extract and mix until smooth. Add half of the milk mixture and mix until just incorporated.
2/3 cup granulated sugar, 1/4 cup canola oil, 1 large egg, room temperature, 1 teaspoon vanilla extract
Sprinkle half of the dry ingredients over the wet ingredients and fold into the batter until just incorporated. Add the remaining milk mixture and mix until mostly incorporated. Finish by sprinkling the remaining dry ingredients into the batter and fold just until no dry streaks remain. Do not overmix the batter - it is ok if there are a few lumps.
Pour the batter equally into the prepared cake pans and bake for 18 to 22 minutes, or until the cakes are golden, spongy to the touch, and a toothpick inserted in the middle comes out clean. Tip - Use a cookie scoop to equally portion the batter into the cake pans.
Cool the cakes in the pans set on a wire rack for 10 minutes. Then gently invert the cake pans onto the wire rack to release the cakes. Carefully peel away the parchment paper (if it stuck to the bottom of the cakes), and flip the cakes back over to cool on the wire rack completely.
Chocolate Swiss Meringue Buttercream
Once the cake is cool, make the frosting. Create a double boiler. Simmer about 2 inches of water in a saucepan. You will then need a heat-proof mixing bowl large enough to sit on the saucepan without touching the bottom. Gather your hand held mixer and attach the whisk attachments. You will also need the regular beaters too.
In a microwave-safe bowl, add the chocolate and melt in the microwave in 30 second increments, stirring after each, until the chocolate is melted. Set aside to cool at room temperature.
2.5 ounces unsweetened chocolate
Add the egg whites to the mixing bowl. Be extremely careful not to get any yolk in the egg whites. Note - The mixing bowl and whisk attachments must be clean and free of any grease or residue. You can wipe them with a paper towel and a tiny bit of vinegar to make sure they are clean.
2 large egg whites, room temperature
Add the sugar to the egg whites and whisk to combine. You can use one of the whisk attachments as your whisk. Set the bowl on top of the saucepan of simmering water. Whisk constantly until the sugar dissolves and the mixture starts to turn white. The egg mixture is ready when it reaches 160F degrees. Or, rub a little of the egg mixture between your fingers - if it is smooth and no longer grainy, it is ready.
1/3 cup + 1 tablespoon granulated sugar
Remove the bowl from the saucepan and with the hand mixer fitted with whisk attachments, beat the egg whites to stiff peaks. This may take anywhere from 3 to 7 minutes. Note - If the egg whites don't reach stiff peaks, chances are either the bowl or beaters were contaminated with oil or residue, or the egg whites had yolk in them. There is no saving them, and you will have to start over.
Once the egg whites have reached stiff peaks, switch to the beater attachments. On medium speed, begin to add the butter 1 tablespoons at a time. Making sure each butter cube is mixed in before adding the next. Once you've added all of the butter, add the cooled melted chocolate and vanilla extract. Continue to beat on medium speed until the chocolate is thoroughly mixed in and the frosting is smooth and creamy.
At this point, the frosting is ready to use right away. Or you can cover the bowl with plastic wrap and refrigerate until ready to use.
Assemble the Cake. Place one cake on a serving plate. Top with the strawberry filling - using as much as you prefer (you may have a little leftover). Place the second cake on top. Frost the cake with the chocolate frosting - either pipe on or simply frost with an offset spatula.
The cake is best enjoyed the day it is made, but can sit covered at room temperature for 1 day. After that, I recommend covering and refrigerating for up to 3 days.
Notes
Frosting Notes
Carefully separate the eggs. Any traces of egg yolk in the whites and the whites won't beat to stiff peaks.
Make sure the whisk beaters and bowl are clean and free of any oil or residue. Wipe down with a little vinegar on a paper towel. The egg whites probably won't beat to stiff peaks if the bowl or beaters are dirty.
The butter shouldn't be too soft, and it should still feel cool to the touch. Butter that is too soft will make the frosting soupy.
If the butter is too soft, and the frosting is soupy, you can refrigerate the frosting for 10-15 minutes to cool it down, before continuing to beat in more butter.
The melted chocolate needs to be cool before adding to the frosting. If it is still too warm, it will probably turn the frosting to soup. Refrigerating the frosting before continuing to beat can remedy this.
The frosting is stable enough to stay at room temperature. However, I don't recommend keeping the cake at room temp for longer than a day because of the filling and frosting - (especially if it is warm out).