Preheat oven to 350°F. Place nine 4-inch shallow paper baking cups onto a large baking sheet and set aside.
Cream butter and both sugars in the bowl of an electric mixer fitted with a paddle attachment for 3 minutes, until fluffy.
Add eggs and vanilla and mix until blended.
Whisk flour, cornstarch, baking powder, and salt in a medium bowl until combined. Slowly add to a mixing bowl on low speed until flour is incorporated.
Add mini chocolate chips and 1/2 cup of chocolate chunks until chocolate is evenly distributed. Do not overmix.
Place 1/2 cup of dough into reserved baking cups, gently pressing dough into the bottom of each cup.
Evenly divide the remaining 1/2 cup of chocolate chunks among cookies and press into the top of the cookies.
Bake for 20 to 25 minutes, or until golden brown. Cool for 5 minutes, then transfer to wire cooling racks.