Preheat the oven to 350 degrees F. Butter 3 (6-inch) round cake pans or 2 (8 inch) round cake pans. Line with parchment paper, then butter.In a medium size bowl, combine the flour, cocoa powder, baking powder, baking soda, and salt.In the bowl of a stand mixer (or use a hand-held mixer) beat together the butter and sugar until light and fluffy. With the mixer on low, beat in the eggs, one at a time, until incorporated. Add the buttermilk, coffee flavored liquor (if using) and vanilla and beat until combined. Slowly add the dry ingredients to the wet ingredients with the mixer on low until just combined. Beat in the hot water. Pour the batter among the cake pans and bake 30-35 minutes, until the tops are just set, and no longer wiggly in the center. Remove and let cool five minutes, then run a knife around the edges of the pan and turn the cakes out onto a cooling rack. Cover and let the cakes cool completely before assembling.To make the ganache. In a microwave safe bowl, combine the heavy cream, butter, and chocolate. Microwave on power lever high for 30 second intervals, stirring after each interval until melted and smooth. Let the ganache cool 5-10 minutes.6. To make the buttercream. Add 1 stick butter to a skillet set over medium heat. Allow the butter to brown lightly until it smells toasted, about 2-3 minutes. Stir often. Remove from the heat and transfer the butter to the mixing bowl, let cool until it's room temp.Add the remaining stick of butter, mascarpone, and powdered sugar. Beat the butter and powdered sugar together until the butter is light and fluffy. Add the vanilla and beat until combined.To assemble. Place 1st cake layer on a serving plate. Spread 1/2 of the ganache over the cake. Add the 2nd cake layer and spread with the remaining ganache. Add the 3rd layer. Frost the outside of the cake with a thin layer of buttercream. Chill 30 minutes and then frost the cake generously with the remaining buttercream. Break the rounded tip off of the candy cane. Dip 1 end of the candy in buttercream to act as the tip of the "pole". Sprinkle the buttercream with pearl sugar. Insert the candy cane off-center on the top of the cake. Sprinkle with pearl sugar for "snow". Decorate as desired. Serve, or store in the fridge for up to 3 days.