Preheat your oven to 350°F/175°C. Grease and line two 8-inch cake pans
In the bowl of a stand mixer with the paddle attachment, mix all of the dry ingredients on slow speed until blended. Add in your butter and mix on low until it looks like damp sand
Add your egg whites one at a time, and then your whole egg. Beat well after each addition, making sure you scrape the sides and bottom of the bowl.
In a small jug, whisk together the bourbon, yogurt and milk
Slowly pour in one-third of the milk mixture into the mixing bowl. With the speed on low, mix together. Be careful as it may spill! Pour in the rest of the milk in two more additions, mixing slowly after each addition. Beat for 2 minutes. Your batter will be liquidy
Pour the batter into your two pans. Bake for 25-30 minutes. A toothpick inserted into the cake will come out clean. Remove from the oven and let cool for 15 minutes. Take the cake out of the tin and let it cool completely
Make Frosting
In a stand mixer fitted with the paddle attachment, beat the butter and powdered sugar together on low speed
Increase the speed to medium-high and beat until it becomes thick
Add the peppermint extract and salt and beat on medium-high
Turn the mixer to low, and pour in the cream until it becomes creamy and spreadable
Make white chocolate drip
Place your chopped chocolate in a medium bowl. Heat up your cream in the microwave for 1-2 minutes, or in a small saucepan over medium heat, until it begins to simmer.
Pour the simmering cream over the chocolate and let it sit for a couple of minutes. Use a rubber spatula to mix the white chocolate and cream together until it is completely smooth. If it isn't hot enough to melt, place it back in the microwave briefly.
Assembly
Place one layer down and spread some of the frosting over it. Place the next layer on top and gently press down. Frost the cake and chill for 10 minutes.
Use a spoon to place the drip over the edge and let it slowly drip down. Repeat all along the cake. If the ganache doesn't drip down, heat it up in the microwave for a few seconds. If the ganache runs down too quickly, then let it sit out for a bit longer. Spoon over the remaining ganache on top and use a small offset spatula to evenly spread the ganache on top.
Notes
My recipes have been developed and tested in metric grams. I highly recommend using a weighing scale and measuring out your ingredients the metric way. I have provided a conversion to US cups but please note that I haven’t tested the recipe with this method. Just click on 'US Customary'. Butter: I use European style butter, like Kerry Gold, in my recipes. This will make your frosting much creamier and richer.Salt: If you don’t have kosher salt, halve the amount of salt called for in the recipe. 1 teaspoon kosher salt = ½ teaspoon fine salt.Peppermint Extract: If you don't like peppermint or don't have it on hand, substitute it for vanilla extract. Storage: Cover the cake tightly and keep in the fridge for up to 5 days. Freezing: Freeze for up to 3 months, let the cake defrost overnight in the fridge and then come to room temperature when you’re ready to eat it.