In a large bowl, use an electric mixer on low speed to combine the butter and sugar followed by the egg yolk. Beat in the flour, cornstarch and salt until the dough is just starting to form. Stir in the chocolate chips and press the dough into a disk. Cover with plastic wrap and chill in the refrigerator for 1 hour until the dough is firm.

Preheat the oven to 275 degrees F. Line 2 sheet pans with parchment paper. Roll out the dough on a lightly floured work surface until it is 1/4-inch thick. Use a 3-inch round cookie cutter to cut out the cookies. Place them on the prepared sheet pans 2 inches apart. Reroll the dough scraps and continue cutting out the cookies.

Bake for 30 minutes until the cookies are firm, but not browned. Cool on the sheet pans for 2 minutes before transferring to a wire rack to cool completely.

Let the ice cream soften at room temperature until it is just scoopable, but not too soft. Use an ice cream scoop to place 1 scoop of vanilla ice cream on half the cookies. Place another cookie on top and press down slightly to sandwich them together. Decorate the sides of the sandwiches with sprinkles and chill in the freezer until firm.