Preheat oven to 350°F. Spray a cupcake pan with non-stick cooking spray.

Cream butter and sugar together until light and fluffy, about 3-4 minutes.

Mix in egg and vanilla extract.

Combine flour, baking soda, cornstarch, and salt. Add to butter mixture and mix until a thick, sticky dough forms.

Form dough into 2 tbsp balls. Press into cupcake cups to form a cup shape.

Bake for 10-12 minutes until edges are golden. Cool in pans, then remove and press centers if needed.

Make pastry cream: whisk egg yolks, then heat milk with sugar and cornstarch until thickened. Temper eggs with milk mixture, then cook until boiling. Remove from heat and stir in butter and vanilla. Chill.

Prepare chocolate ganache: heat heavy cream and corn syrup until boiling, pour over chocolate chips. Let sit, then whisk until smooth. Chill until firm.

Assemble: Fill cookie cups with pastry cream, top with ganache. Chill until serving.