Preheat oven to 400 F. Line baking sheet with parchment or silpats (see note) and set aside.

Combine water, milk, sugar, salt, and butter in a medium saucepan. Bring to a boil over medium-high heat.

Once boiling, and while still on the heat, add the flour. Quickly beat mixture with a wooden spoon until smooth and shiny. Mixture will pull away from the sides of the pan. (Do not underbeat or cream puffs may deflate later!)

Once mixture is thoroughly combined, scrape it into the bowl of a stand mixer. Turn the mixer on low speed. With mixer running, add eggs one a time, allowing each egg to incorporate and mixture to become smooth before adding the next.

Transfer batter to a pastry bag and cut a hole in the end (about ⅓" across). Pipe mounds of choux pastry at least 2" apart, each about 2" across and ¾" tall (see notes). With those dimensions, you get about 24 cream puffs.

Place the baking sheet in the oven and turn the oven off. Bake 10 minutes with the oven off. Turn oven back on to 350 F and bake another 10 minutes. Then, turn the oven off again, leaving the cream puffs to finish baking for another 10 minutes (This is 30 minutes in the oven total). Resist the urge to open the oven until baking is complete, as this could deflate your cream puffs!

Once the cream puffs are baked, remove from the oven and poke a hole in the top of each with a toothpick. This will allow any residual steam to escape (otherwise, your cream puffs could deflate...sensing a trend here?). Allow cream puffs to cool completely.

Preheat oven to 350° F. Spread the flour out on a baking sheet in an even layer. Toast 5-7 minutes. Remove from the oven and cool completely (see note).

In the bowl of a stand mixer, combine the butter and sugars. Beat until light and fluffy, at least 3 minutes.

Add vanilla and salt. Mix to combine. Add (toasted) flour and cream. Beat until incorporated and fluffy, 3-5 minutes. Add mini chocolate chips and stir to incorporate. Cookie dough will be soft and fluffy.

Combine chocolate and cream in a small heatproof bowl and microwave on 30-second burst, stirring after each burst, until the mixture is smooth.

Split the cooled the cream puffs with a thin, serrated knife.

Spoon or pipe the cookie dough into the bottom of each of the cream puffs. Place the tops of the cream puffs on the filling, then drizzle (or drench!) with the ganache. It's best to assemble the cream puffs as close to when you plan to serve them as possible.Enjoy!