Step 1: Prepare Cake Mixture. Melt white chocolate with milk, stir until smooth, mix in espresso powder and cool slightly. Whisk together flour, baking powder, and salt. Cream butter with sugar, add eggs and vanilla, then mix in flour and chocolate mixtures.

Step 2: Bake the Cake. Preheat oven to 350°F and grease cake pans. Divide batter among pans, smooth tops, and bake for about 40 minutes until a toothpick comes out clean. Let cool for 10 minutes before transferring to a wire rack.

Step 3: Make Buttercream. Place egg whites and sugar in a bowl over simmering water, whisk until warm. Beat in a mixer until stiff peaks form, then add butter and espresso powder until smooth.

Step 4: Prepare Ganache. Heat cream until hot, remove from heat and stir in white chocolate until smooth. Let cool until thick and pourable.

Step 5: Assembly. Place a cake layer on stand, spread ganache, add another layer, repeat, and frost with buttercream. Pour ganache over top to create a drip effect.

Step 6: Decorate. Use decorative elements for a festive touch, chill for 30 minutes before slicing.