adapted just a bit from Life (Made) Simple
2 cups all-purpose flour
1½ cups quick rolled oats
1 cup sugar
1 cup light brown sugar
1 cup peanut butter
1 cup butter
1 tsp. vanilla extract
1 tsp. baking soda
½ tsp. salt
½ cup peanut butter
2 cup powdered sugar
5 Tablespoons milk
1½ cups chopped Reese's peanut butter cups (about 30 miniature ones)
Preheat oven to 350 degrees. Lightly grease a full size cookie sheet. In the bowl of a stand mixer, beat together peanut butter, butter and sugars for 30 seconds. Turn speed to low and add one egg at a time. Add vanilla and mix until combined.
Fold in dry ingredients. Do not overmix. Pour into prepared pan and pat down until even.
Place in oven and bake for 15-20 minutes, or until the top begins to brown.
Meanwhile, prepare topping buy beating powdered sugar, peanut butter and milk in a small bowl. Chop peanut butter cups up.
Remove bars from oven and place pan on a wire rack. Immediately spread topping over warm bars (it will become melty and shiny). Sprinkle with chopped peanut butter cups. Allow to cool completely before cutting into bars.