For the shells:
200 gr powdered sugar
55 gr almonds (slivered, blanched, sliced, whatever you like)
55 gr pistachios (roasted, unsalted)
90 gr egg whites (use egg whites that have been preferably left 3-4 days in the fridge)
25 gr granulated sugar
1/2 cup cocoa nibs

For the buttercream:
3 egg yolks
1/2 cup sugar
1/4 cup water
1 1/2 sticks unsalted butter, at room temperature
2-3 tablespoons Bourbon