adapted from Bouchon Bakery for Bozeman Montana altitude, approx. 5000 ft.
makes 12
This recipe requires a 2 hour rest of the dough after mixing and before baking and uses a specialty pan sold by Williams Sonoma. It is called either a "petite popover" or "bouchon" pan and is made in metal and silicone versions. If you use the metal pan, spray the molds with baking spray. You do not need to grease silicone molds but some people recommend it to make cleanup easier.
Cut butter into pieces, melt half and put remaining half in a bowl. Pour melted butter into the bowl and stir until all remaining pieces have melted. Set aside.
Put flour in a bowl and sift cocoa powder over it. Sprinkle with salt. Whisk to combine.
In an electric mixer with the whisk attachment, whisk eggs for a minute then with the mixer running, add sugar in a slow stream and continue to whisk for a couple minutes. Add vanilla and mix. In 3 alternating additions, add the butter and flour. Remove bowl from mixer, scrape down edges and bottom, and stir to make sure everything is combined. Stir in the chocolate chips.
Set batter aside for 2 hours at room temperature (do not refrigerate).
Preheat oven to 375°F.
Transfer batter to a piping bag or spoon carefully into prepared pan. Place pan in oven, reduce heat to 365°F and bake for 12–14 minutes, until tops are rising above the mold and beginning to dry around the edges. Remove from oven and set pan on cooling rack for 10 minutes then flip to unmold, they should pop right out. Sprinkle tops with powdered sugar just before serving.