Whisk flour, cocoa, sugar, and salt together in a bowl.
Add eggs, milk, melted butter, and vanilla; mix until smooth.
Heat a nonstick crepe pan over medium heat and lightly grease.
Pour a ladle of batter, swirl to coat, and cook 1 minute per side.
Cool crepes completely, stacking with parchment between layers.
Whip cream with powdered sugar to soft peaks; fold melted chocolate into half.
Pipe alternating white and chocolate cream onto each crepe and stack.
Heat cream, pour over chopped chocolate, and stir into smooth ganache.
Spread ganache over the top and sides of the cake.
Press sliced almonds onto the sides, dust the top with cocoa, chill, and slice.