1Heat oven to 350°F. Spray 13x9-inch pan with baking spray with flour. In small bowl, stir flour, baking powder and salt; set aside.
2In medium microwavable bowl, place butter and peanut butter. Microwave on High 30 to 45 seconds or until butter is melted. Add brown sugar and egg yolk; stir until mixed. Stir in vanilla and flour mixture. Stir in 3/4 cup of the chocolate chips. Spread in pan.
3Bake 20 to 25 minutes or until just firm to the touch. Remove from oven; immediately sprinkle with remaining 1 1/4 cups chocolate chips. Let stand 2 to 3 minutes or until chips have softened. Spread softened chips evenly over top. Sprinkle with peanuts. Cool on cooling rack. Cut into 8 rows by 6 rows. Store in airtight container.