Combine the cocoa, powdered sugar, flour, butter and egg yolk in the bowl of a food processor. Pulse and process until the mixture form a ball of dough.
Divide the dough between six (4 ½-inch) tart pans with removable bottoms. Press the dough evenly into the pans using your fingers taking care to fill the indentations in the sides of the pans. Place the tarts on a rimmed cookie sheet. Using the tines of a fork, pierce the bottom of each crust a few times then refrigerate for 30 minutes.
Bake for 12 minutes or until the crust is set. Cool completely before filling.
Notes
If the crust bubbles up or is puffy after baking, gently press the crust with the back of a spoon.
Store at room temperature until ready to fill. May be made a day ahead.
One package of the Royal Delights White Chocolate Dessert Mix fits perfectly into these 6 pie shells. Mix according to package directions with 1 cup of milk.
Nutrition information is calculated using an ingredient database and should be considered an estimate. When multiple ingredient alternatives are given, the first listed is calculated for nutrition. Garnishes and optional ingredients are not included.