Preheat oven to 400°.

In a large bowl, beat butter and sugars until blended. Beat in egg and vanilla.

In another bowl, whisk flour, cocoa and baking soda; gradually beat into creamed mixture.

Shape level tablespoons of dough into 2-1/2-in.-wide patties. Press onto bottoms and up the sides of greased mini-muffin cups.

Bake until set, 8-10 minutes. Immediately press a deep indentation in center of each with the end of a wooden spoon handle.

Cool in pans for 5 minutes. Remove to wire racks to cool completely.

For filling, in a small heavy saucepan, combine chocolate chips, cream and butter; cook and stir over medium heat until smooth. Remove from heat.

In a small bowl, whisk a small amount of hot mixture into egg yolks; return all to pan, whisking constantly.

Cook over low heat, stirring constantly, until mixture is thickened and a thermometer reads at least 160°, 15-17 minutes. Do not allow to boil.

Immediately transfer filling to a bowl; cool for 20 minutes, stirring occasionally.

Spoon 1 tablespoon filling into each crust. Top with sprinkles.

Refrigerate until cold, about 1 hour.