Preheat the oven to 350°F / 175°C and line a muffin pan.
Whisk 1 1/4 cups all-purpose flour, 1 cup Domino® Granulated Sugar, 1 1/2 tsp baking powder, and 1/2 tsp salt together in a large bowl.
Make a well in the middle of the dry ingredients and add 1/2 cup of sour cream, 1/2 cup water, 1/4 cup vegetable oil, 1 large egg, and 1 Tbsp vanilla extract into the opening. Whisk the wet ingredients together, then whisk them into the dry ingredients. Mix until the batter is smooth.
Divide the batter evenly between the cupcake liners, filling them about 3/4 of the way full. Bake for 18-20 minutes or until a toothpick comes out with a few moist crumbs.
Let the cupcakes cool for 10 minutes before moving them to a cooling rack to finish cooling. If you want to accelerate the cooling process, pop the pan into the freezer for about 30 minutes.
Vanilla Buttercream
While the cupcakes bake and cool, make the vanilla buttercream. In a large bowl or the bowl of a stand mixer, beat 2 cups of room-temperature butter on a medium speed for 30 seconds with a hand mixer or paddle attachment until smooth.
Add 2 tsp vanilla extract and 1/2 tsp salt and mix on a low speed.
Mix in 7 cups of Domino® Powdered Sugar and 1/4 cup of heavy cream on a low speed until combined. Scrape the bottom and sides of the bowl with a rubber spatula as needed.
Mix on low until the ingredients are fully incorporated and the desired consistency is reached. If the frosting seems too thick, add an extra Tbsp of heavy cream. If it's too thin, add another 1/4 cup of powdered sugar.
Stir by hand with a rubber spatula for a couple of minutes to make the frosting SUPER smooth.
Use gel food coloring to color 3/4 cup of the frosting pink and 3/4 cup of the frosting blue. Place the pink and blue frosting in their own small piping bags fit with small French piping tips.
Place the remaining white frosting in a large piping bag. Snip a small opening (about 1 cm) at the base of the bag and set aside.
Decorating These Mini Gender Reveal Cakes
Unwrap one of the cupcakes. Use a sharp knife to cut the cupcake into two horizontal layers. Spread a dab of frosting onto a small, greaseproof cake board. This will help keep the cupcake stack in place on the board.
Place the bottom half of the cupcake in the center of the board. Spread an even layer of blue or pink (blue for a boy, pink for a girl) frosting on top of it, then top it with the upper half of the cupcake. Freeze the stacked cupcakes for 5-10 minutes, until the stack is firm to the touch.
Cover the cupcake stack in a thin layer of white frosting and smooth using a small offset spatula. Freeze the stacked cupcake for an additional 5-10 minutes, until the frosting is firm to the touch.
Then spread on a second, thicker layer of white buttercream. Pipe small dollops of pink and blue frosting around the base of the cake and use a small offset to create vertical streaks of frosting up the side of the mini cake.
Pipe swirls of pink and blue buttercream in a ring on top of the cake. Repeat with the remaining cupcakes, then chill them until you're ready to cut into them.
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Notes
Ingredient Swaps & Substitutions
For a detailed list of ingredient swaps and substitutions that can be made in each component of this recipe, please refer to the "swaps and substitutions" section above.
Tips for Making the Best Mini Gender Reveal Cakes
Ingredients at room temp mix together better. Set out any cold ingredients ahead of time.
Properly measure your flour (spoon into the cup measure and then level) or use a kitchen scale to measure your dry ingredients.
Once you add the flour, mix the cupcake batter just until the ingredients are incorporated. This will ensure the cupcakes bake up tender and fluffy.
Use a large cookie scoop to fill your cupcake liners easily. It also makes sure the cupcakes end up being the same height.
Seal off the top of your piping bag with a rubber band to prevent any frosting from seeping out the top of the bag and make the piping bag easier to use.
Gluten-Free Variation
To make gluten-free mini gender reveal cakes, swap in your favorite gluten-free flour blend for the AP flour this recipe calls for. Be sure to over-mix your batter and let it sit for at least 30 minutes before baking for best results.
Making These Mini Gender Reveal Cakes in Advance & Storage Tips
You can make these mini cakes in advance! Frosted mini cakes can sit at room temperature for a day or be stored in the fridge for up to 5 days in an airtight container.You can make the buttercream ahead of time too or save any leftovers. This buttercream frosting will last in the fridge for up to a month.Be sure to stir the frosting well once it thaws to make the consistency nice and smooth again. You can also store buttercream in a piping bag in the fridge. I find buttercream keeps its consistency well in piping bags and doesn't require any mixing after it's thawed.