In a separate bowl, add the flour, baking soda, cornstarch, baking powder, salt, and quick oats; whisk to combine. With the mixer on low speed, slowly add the flour mixture to the wet ingredients and mix until just combined. Stir in the chocolate chips and REESE’S Pieces candies by hand.
Measure out ¼ cup balls of dough and place them on the baking sheets. Bake the cookies for 11-13 minutes, until the edges are just starting to brown and the top still looks slightly undercooked. Remove from the oven and cool for 5 minutes on the baking sheet before moving them to a wire rack to cool completely. Before these have cooled completely, they will be crumbly. I suggest letting them cool completely before tasting.
As written, this recipe makes 12 very large cookies. You can certainly make 24, more normal-sized cookies.
3-4 minutes will seem like a long time to mix the sugars, peanut butter, and butter but it's really important. The dough will become much lighter in color and look fluffy. That's when you know you have blended it long enough.
For a flatter cookie, take the bottom of a drinking glass and gently press down on the cookie right after they come out of the oven OR just press some additional candies on the tops of the cooked cookies and that will naturally press them down into more of a cookie shape, I always do this and it works so well. The cookies don't spread much at all while baking.
Natural peanut butter does not work well in this recipe. I used the original Jif.
Press some additional candy pieces and chocolate chips on top of the cookie dough balls, before putting cookie sheet in the oven, for a pretty presentation.
Freezing Instructions: Baked and cooled cookies freeze well for up to 3 months. Unbaked cookie dough balls freeze well for up to 3 months too. Bake frozen cookie dough balls for an extra minute, no need to thaw.