Preheat your oven to 375 degrees F. Line a baking sheet with parchment paper. Set aside.
Combine the flour, sugar, and cocoa powder in a medium mixing bowl. Set aside.
Melt the butter in a medium saucepan over medium heat. Add the water and bring to a rolling boil.
Pour in the flour mixture and continue to stir until the dough starts to come together. The dough will become a ball, but keep stirring over heat for 1 minute.
Transfer the dough to the bowl of a stand mixer. (see note) Turn the mixer to medium speed and beat the dough for 2-3 minutes, allowing it to cool slightly. Add the eggs one at a time as you continue to let the mixer run. (The dough will become creamy and smooth.)
Place 1 tablespoon scoops of the dough onto the prepared baking sheet spacing them at least 1 inch apart.
Bake for 20 minutes. Remove from the oven and allow the puffs to cool completely on a wire rack.
Chocolate Cream Filling
In a large mixing bowl, whisk the pudding mix and milk together until thickened and smooth, about 2 minutes. Whisk in the sour cream until completely incorporated.
Cover with plastic wrap and place in the refrigerator for 1 hour.
Assembly
Method 1: Slice the puffs in half. Pipe the filling onto the bottom half, place the top of the cream puffs in place (like a sandwich), and dust with powdered sugar.
Method 2: Transfer the cream filling to a pastry bag with a pointed tip. Carefully stick the tip into a puff and fill it with the chocolate cream. Dust the tops with powdered sugar.
Notes
If you don't have a stand mixer, transfer the dough to a large mixing bowl and use a hand mixer to incorporate the eggs.