1. Prepare the Cupcake Batter

Preheat your oven to 350°F (175°C) and line 18 cupcake cups with paper liners. This will ensure the cupcakes bake evenly and don’t stick to the pan. Set the lined pans aside for now.

In your electric mixer, beat the egg whites until they form stiff peaks. This will give your cupcakes the light, airy texture we’re aiming for. Once done, set the egg whites aside.

In a separate bowl, cream together the butter and sugar. Beat them until the mixture is light and fluffy, which should take about 3-4 minutes. This step is essential to creating a soft and tender crumb for your cupcakes. Make sure your butter is at room temperature before you start, as cold butter can cause the sugar to not incorporate properly.

Next, sift the dry ingredients: flour, baking powder, and salt. Sifting ensures that there are no lumps in your dry ingredients, giving you a smoother batter and a better texture for the cupcakes. Whisk them together to ensure even distribution.

Now, slowly combine the dry ingredients into the butter and sugar mixture, alternating with the champagne or prosecco. You can start by adding a small portion of the dry mixture, followed by a bit of champagne. Repeat this process until everything is combined. Gently fold in the diced peaches. The champagne will add a touch of sparkle to the batter and help create a moist, tender cupcake.

Fold the egg whites into the batter in three additions. This part requires a light touch—be careful not to deflate the air you’ve worked so hard to whip into the egg whites. Folding the egg whites gently will help the cupcakes rise and stay light and fluffy.

Once everything is combined, spoon the batter into the cupcake liners, filling them about 2/3 full. This will give the cupcakes room to rise without overflowing. Bake for 18-22 minutes, or until a toothpick inserted into the center comes out clean. Allow them to cool in the pan for 5 minutes, then transfer them to a wire rack to cool completely. It’s important to let the cupcakes cool before filling them with the pastry cream, so don’t skip this step.

2. Make the Champagne Pastry Cream

While the cupcakes are baking, let’s prepare the champagne pastry cream that will be tucked inside each cupcake.

In a medium bowl, whisk together ¼ cup heavy cream and the cornstarch. This will help thicken the mixture once it’s cooked. Add the whole egg and egg yolks, whisking to combine. The eggs will give the pastry cream its richness and help it set as it cools.

In a saucepan, combine the remaining heavy cream, sugar, and champagne. Bring the mixture to a boil and then remove it from the heat. Slowly pour about one-third of the hot mixture into the egg mixture while whisking constantly to prevent curdling. This is called tempering the eggs, and it ensures that the eggs won’t cook too quickly when combined with the hot liquid.

Once combined, return the saucepan to the heat and add the egg mixture back in, pouring it slowly and whisking continuously. The cream should begin to thicken as it heats. Once thickened, remove from heat and stir in the butter and vanilla. The butter will make the pastry cream silky and smooth, while the vanilla adds a lovely depth of flavor. Allow the pastry cream to cool to room temperature. Cover the surface of the cream with plastic wrap to prevent a skin from forming. Store in the fridge until needed.

3. Prepare the Peach Buttercream

For the peach buttercream, beat the softened butter and confectioners’ sugar together in your electric mixer until light and fluffy. Gradually add a small amount of milk or cream to achieve a smooth, piping consistency. Be patient with this step and add the liquid gradually so that you don’t end up with a runny frosting.

Add the peach flavoring oil (or peach schnapps) and mix well. Now, it’s time to color the buttercream. Add neon yellow and neon orange food coloring to achieve a vibrant peach hue. This step is entirely up to you, and you can adjust the colors until you’re happy with the result. For a bit of flair, you can even add a drop of red food coloring to intensify the peach color.

Once your buttercream is beautifully colored and fully mixed, prepare your piping bag. Place a little red food coloring inside the piping bag using a brush, then pipe the frosting onto each cupcake in a swirling motion. This technique adds a touch of creativity and will give your cupcakes a professional finish.

4. Assemble the Cupcakes

It’s time for the fun part—putting it all together!

Use a paring knife to core the center of each cupcake. The divots you create will hold the champagne pastry cream. Transfer the cooled pastry cream to a piping bag and fill each cupcake with about 1 ½ to 2 tablespoons of the cream. Don’t overfill the cupcakes, as you still need room for the frosting on top.

Once the cupcakes are filled, replace the tops of the cupcakes to create a lid over the filling. This will keep the pastry cream inside and give the cupcakes a nice rounded shape.

Finish off each cupcake by piping the peach buttercream on top in a decorative swirl. Sprinkle with white nonpareils for a touch of sparkle, and add a fresh mint leaf for an extra pop of color. The mint leaf is optional, but it adds a nice fresh contrast to the sweetness of the cupcakes.