Line a large baking sheet with parchment paper and set aside.

In the bowl of a stand mixer fitted with the paddle attachment, mix together the butter, light brown sugar, and granulated sugar on medium speed for 3 minutes.

Add in the eggs, vanilla, baking soda, salt, and cornstarch and mix for 1 minute, scraping down the sides of the bowl as necessary.

Turn the mixer to low and mix in the flour until just combined. Fold in the chocolate and peanut butter chips.

Refrigerate the dough for 1 hour.

Preheat oven to 375°F.

Portion out a rounded ¼ cup of cookie dough and roll into a ball. Break the cookie dough ball in half, turn the dough so the jagged broken edges are facing up and then press back together to create a craggily top.*

Place the cookie dough onto the prepared baking sheet at least 3-inches apart (about 6 will fit on a standard baking sheet).

Bake for 16 minutes, until the edges and top are slightly golden. Do not over-bake.

While still warm, press one Reese’s thin into the center of each cookie as well as additional chocolate and peanut butter chips. Allow to cool on the cookie sheet for at least 5 minutes and then transfer to a wire rack to cool completely.