Preheat the oven to 425°F. Lightly grease (or line with parchment) two baking sheets.

Combine the water, butter, sugar and salt in a medium-sized saucepan, heat until the butter has melted, and bring to a rolling boil. While heating mix together flour and cocoa powder.

Remove the pan from the heat, and add the flour and cocoa powder mixture all at once, stirring vigorously.

Return the pan to the burner and cook over medium heat, stirring all the while, until the mixture smooths out and follows the spoon around the pan; this should take less than a minute.

Remove the pan from the heat, and let the mixture cool for 5 to 10 minutes. It'll still feel hot, but you should be able to hold a finger in it for a few seconds. If you have an instant-read thermometer, the temperature should be below 125°F.

Transfer the mixture to a mixer, and beat in the eggs one at a time; it'll look curdled at first, but when you add the last egg it should become smooth. Beat for at least 2 minutes after adding the last egg.

Using a generously filled cookie scoop for mini puffs ( or you can use a heaping Tablespoon), or a level muffin scoop for larger puffs, drop the thick batter onto the prepared baking sheets. Space the mounds about 3" apart, to allow for expansion. Smooth out any spikes in the dough gently with a spoon dipped in cold water.

Bake the pastries for 15 minutes, then reduce the oven temperature to 350°F and bake for an additional 15-20 minutes, until pastries are set and firm to touch (will take 20-25 min for the larger cream puff shells). Don't open the oven door while the pastries are baking.

Remove the pastries from the oven. Make a small slit in the top of each, and return them to the oven for 5 minutes, to allow the steam to escape. Place them on a rack to cool. When they're cool enough to handle, split each in half to make top and bottom pieces; splitting and exposing the centers to air will help keep them from becoming soggy. (If you want to wrap and freeze them, don't cut them in half first)

To store: loosely cover and store at room temperature for a few days or wrap and freeze until ready to use.

Heat half and half and 6 Tbsp of the sugar in a medium saucepan over medium heat, stirring occasionally to dissolve sugar, until mixture comes to a simmer.

Meanwhile place egg yolks in a medium bowl and whisk until smooth. Add sugar and whisk to combine. Add cornstarch and whisk until combined and pale yellow (about 30 seconds).

Once half and half is simmering, slowly stream half the mixture into the egg yolk mixture,whisking constantly (to temper the eggs). Then add this tempered egg mixture back into the saucepan while whisking constantly (you don't want scrambled eggs). Continue to stir until mixture is thickened and glossy and bubbles burst on the surface.

Pour this mixture into a bowl through a fine mesh strainer (to remove any lumps). You will probably have to press it through with a spatula.

Immediately and thoroughly whisk in butter and vanilla. Then whisk in peanut butter until smooth. Cover with plastic wrap, gently pressing it into surface so no skin will form and place in fridge to cool, at least 4 hours. (To cool quicker, spread pastry cream in a 9 x 13 pan)

Once completely cooled stir about 1/4 of the whipped cream in to lighten up the mixture then gently fold in the remainder until no streaks remain.

In a microwave safe dish heat chocolate with 4 Tbsp of the heavy cream- I usually heat it on half power for about a minute, stir then heat in 15 second intervals, stirring in between, until the chocolate is melted and smooth. Then add in the peanut butter, stirring until combined. Add additional cream to desired consistency.

Fill the bottom half of each pastry shell generously with desired amount of pastry cream, place top half on and drizzle with the warm ganache. Let the ganache set a bit then serve right away for best results or they can be refrigerated for several hours. (I usually assemble only the amount we will eat at that time)

Note*** you probably will have some pastry cream left over- Eat it as a pudding/mousse or be creative. It keeps in the fridge for several days before the cream separates.