Heat oven to 350. Grease bottom and sides of 15 x 10 x 1 inch pan with shortening or spray with cooking spray.
In large bowl, beat sugar, butter, 2 eggs, 1 t. vanilla, the flour, cocoa, oats, and baking powder with mixer on medium speed until well mixed. Stir in peanuts. In small bowl, reserve 1 1/2 cups oat mixture for topping. Press remaining oat mixture on bottom of pan to form crust.
In medium bowl, beat cream cheese on medium speed until smooth. Add 3 eggs, the milk, peanut butter, and 1 t. vanilla. Beat on medium speed, scraping bowl occasionally, until well mixed. Spoon peanut butter mixture over oat mixture in pan; spread evenly to edges of pan. Carefully crumble reserved oat mixture evenly over peanut butter layer.
Bake 35-45 minutes or until toothpick comes out clean. Cool completely in pan on wire rack, about 30 minutes. For bars, cut into 8 rows by 6 rows. Store covered in the refrigerator.