Begin by melting white chocolate in a medium saucepan over low heat, stirring in milk and espresso powder until smooth. Remove from heat and cool.

Preheat your oven to 350°F (175°C) and prepare three 6-inch cake pans by greasing and dusting.

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

Cream together butter and sugar until light and fluffy, about 3-4 minutes. Add eggs one at a time, followed by vanilla.

Gradually add the cooled chocolate mixture to the creamed butter and sugar, mixing on low speed, then alternate adding dry mixture until just combined.

Divide the batter among cake pans and bake for about 40 minutes or until a toothpick comes out mostly clean.

Allow cakes to cool in pans for about 10 minutes before turning out onto a wire rack to cool completely.

For buttercream, combine egg whites and sugar in a heatproof bowl over simmering water until sugar dissolves, then whip until stiff peaks form. Gradually mix in butter and espresso powder until smooth.

Combine white chocolate and heavy cream in a heatproof bowl, heating until smooth. Allow to thicken at room temperature.

Layer the cooled cake rounds with ganache and buttercream, then use remaining ganache for a crumb coat and chill for 20 minutes.

Frost the outside with espresso buttercream, drizzle ganache over the top, and decorate with coffee beans and nonpareils.