In a stand mixer, cream together room temperature unsalted butter and both granulated and brown sugars on medium-high speed for about 5 minutes, until light and fluffy. Gradually add the large eggs one at a time, beating well after each addition, then mix in the vanilla extract until fully combined.

Sift together all-purpose flour, cornstarch, baking soda, baking powder, and salt in a separate bowl. Gradually incorporate this dry mixture into the wet ingredients on low speed, mixing until just combined. Be careful not to overmix.

Gently fold in the semi-sweet chocolate chips and Easter sprinkles to the cookie dough using a spatula. Mix until evenly distributed.

Using a 4 oz cookie scoop, portion out 8 dough rounds. Flatten each round slightly, place a Peep in the center, and carefully shape the dough around the marshmallow to completely enclose it.

Place the stuffed dough balls on a baking sheet and refrigerate for at least 2 hours, or up to 48 hours.

Preheat your oven to 375°F (190°C) and line baking sheets with parchment paper. Bake four cookies at a time for 14 to 16 minutes until edges are golden and tops are lightly set.

Allow cookies to cool on the baking sheet for 20-30 minutes. After cooling, transfer the cookies to a wire rack to cool completely.