To prepare the pate a choux, in a small pot, heat the butter, ½ cup water, sugar, and salt over medium heat until the butter is melted and the mixture comes to a simmer.
Reduce the heat to low, add the flour and cocoa, and cook, stirring, until a smooth dough forms.
Transfer the dough to the bowl of a stand mixer fitted with a paddle attachment and beat in eggs, one at a time.
Transfer the batter to a piping bag fitted with a medium round tip.
Preheat the oven to 375 F.
Line a baking sheet with parchment paper.
Pipe 1-inch mounds of batter onto the baking sheet, spacing them at least 1 inch apart.
Wet your finger and press down to smooth out any kisses on top of the mounds.
Once the oven is preheated, bake for 30-35 minutes until the cream puffs are firm and light in weight.
Cool completely, then slice the tops to separate.
To prepare the cream filling, whip the cream, confectioner’s sugar, cocoa powder, and salt to stiff peaks.
Fold in mini chocolate chips if desired.
Transfer the mixture to a piping bag (fitted with an open star tip if you have one) and chill until ready to use.
To prepare the ganache, in a microwave-safe container, heat the chocolate, cream, and salt in short spurts, stirring to combine until smooth.
Open up the cream puffs, placing the tops next to the bottoms.