Preheat the oven to 350 degrees.

Line a 9x13 baking dish with parchment paper and spray liberally with cooking spray.

In the bowl of a stand mixer, beat together the butter and sugars until light and creamy, about 5 minutes.

Beat in the vanilla and eggs, one at a time, until thoroughly combined.

In a small bowl, combine the flour, baking soda, and salt.

Gradually add the flour mixture to the butter mixture, beating well.

Stir in your candy mix-ins until combined.

Use your hands to press the dough into the baking dish.

Bake for 30 - 35 minutes, checking for the doneness you prefer. (I like them a bit gooey.)