In a medium saucepan, heat the milk and chopped white chocolate over medium heat, stirring until melted and smooth. Whisk in instant espresso powder until fully dissolved. Allow to cool.

In a large mixing bowl, whisk together the flour, baking powder, and salt. Set aside.

Cream together unsalted butter and granulated sugar for 3-5 minutes until light and fluffy. Add eggs one at a time and then vanilla extract.

Gradually add the cooled chocolate mixture to the creamed mixture, alternating with the dry ingredients until just combined.

Preheat oven to 350°F (175°C) and grease the cake pans. Pour batter into pans and bake for 35-40 minutes until a toothpick comes out clean. Cool for 10 minutes before transferring to a wire rack.

Prepare the buttercream by heating egg whites and sugar until dissolved, then whip until stiff peaks. Gradually add butter and espresso powder until smooth.

For the ganache, heat heavy cream until simmering, then whisk in chopped white chocolate until smooth. Allow to cool until slightly thickened.

Assemble the cake by layering the ganache between cooled cake layers, frosting with buttercream, and finishing with ganache drizzles and decorations.