1. Heat oven to 350°F. Grease bottom of 13x9x2-inch baking pan.
2. Place peanut butter chips and peanut butter in microwave-safe bowl. Microwave at MEDIUM (50%) 1 minute; stir. If necessary, microwave at MEDIUM an additional 15 seconds at a time, stirring after each heating, just until chips are melted when stirred.
3. Combine flour, brown sugar, butter and peanut butter chip mixture in large bowl. Beat on low speed of mixer until mixture resembles small crumbs; reserve 1 cup crumbs for topping. To remaining crumb mixture gradually blend in baking powder, baking soda, milk, eggs and vanilla; beating until well combined. Pour batter into prepared pan; sprinkle top evenly with reserved crumbs.
4. Bake 35 to 40 minutes or until wooden pick inserted in center comes out clean. Cool completely in pan on wire rack. 12 to 16 servings.