Moist, peanut butter-y, a little crunchy, sweet but not too sweet — that's how we describe these REESE'S Peanut Butter Cookie Bars. Chopped REESE'S Peanut Butter Cups and REESE'S PIECES Minis are baked throughout a dense, delicious and chewy cookie bar base.
Heat convection oven to 300°F (standard oven: 350°F). Lightly spray one 18x26-inch full sheet pan with vegetable cooking spray. Place parchment paper on prepared sheet pan.
Mix butter, sugar, water and vanilla in 20 qt. bowl of mixer fitted with paddle attachment until creamy. Add eggs; mixing until fully incorporated. Blend together flour, baking powder and salt in large bowl. Gradually add to butter mixture, mixing until well blended. Stir in Chopped REESE'S Peanut Butter Cups and 12 oz. (1-1/2 cups) REESE'S PIECES Minis. With floured hands, press evenly into prepared pan.
Bake 10 minutes. Top with remaining REESE'S PIECES Minis. Bake additional 15 to 25 minutes* or until golden brown. Cool in pan on wire rack. Cut into 2-1/2-inch bars.
Step 3: If using convection oven, rotate sheet pan one-half turn (180°) after 10 minutes of baking.