First, start on the buttercream. In a small pot, heat the butter and white chocolate together until melted. The mixture will look greasy and separated, but it's okay! Whisk everything together, then remove pot from heat and let the mixture come to room temperature. When it is cool enough to handle, transfer to the fridge and chill until completely solid.

Meanwhile, preheat the oven to 350F. Grease two 9-inch round cake pans, line bottoms with parchment paper, and grease paper. Dust pans with cocoa powder.

In medium bowl, whisk together flour, cocoa, baking powder, baking soda, and salt. In a measuring cup, mix together milk and vanilla. In a stand mixer, at low speed, beat butter and sugar till blended. Increase speed to high and beat for 2 minutes. Reduce speed to medium-low and add eggs one at a time, beating well after each addition.

With mixer at low speed, alternatively add the flour mixture and the milk mixture, starting and finishing with the flour. Beat until batter is smooth, occasionally scraping bowl with a spatula.

Pour batter into prepared pans; spread evenly. Bake until toothpick inserted in center comes out clean, 25-30 minutes.

Cool cakes in pans on wire racks for 10 minutes. Run thin knife around edges to loosen cakes from pans, then invert onto wire racks. Remove parchment paper, allow to cool completely.

While cakes cool, prepare the filling. Place the sandwich cookies in a plastic baggie, and using a rolling pin, crush them finely.

In a medium bowl, beat the softened butter until light and fluffy. Add in the powdered sugar a cup at a time, until fully incorporated, then add in the peppermint extract and crushed cookies. Beat together, then add the heavy cream. You can use more or less as needed to make the filling creamy and light! Add salt to taste.

Now, you are ready to start assembling! Choose a serving platter, cake stand, or cardboard cake plate where you will build your cake, and spread a small amount of filling on it. Place one of the cakes on top, then spread the rest of the filling atop this cake. Place the other cake on top of the filling, making sure to orient the flatter, smoother edge up. Make sure cake is flat and level!

Grab the solidified butter and chocolate mixture from earlier, and transfer it to a stand mixer fitted with a whisk attachment. Beat the mixture until it's light and fluffy, and no solid chunks remain.

Using an offset spatula {or whatever decorating tool you prefer}, frost the cake as desired. I simply did one smooth coat! Decorate the sides of the cake with crushed candy cane pieces, and top with pieces of peppermint bark. Refrigerate cake for at least 30 minutes before serving, and enjoy!