2 1/4 cups flour
2 cups packed brown sugar
1 cup creamy peanut butter
1/2 cup butter, room temperature
1 cup milk
1 tsp. vanilla
1 tsp. baking powder
1/2 tsp. baking soda
2 cups semi-sweet chocolate chips
Preheat oven to 350º F. Butter a 13x9x2 inch metal baking pan.
Combine first 4 ingredients in large bowl. Using electric mixer, beat on low speed until streusel is blended and crumbly. Transfer 1 cup lightly packed streusel to small bowl and reserve. Add eggs, milk, vanilla, baking powder and baking soda to remaining streusel in large bowl. Beat at low speed until evenly moist. Increase speed to medium and beat until well blended, scraping bowl occasionally, about 3 minutes. Stir in 1 cup chips. Transfer batter to prepared pan. Sprinkle with reserved 1 cup streusel and remaining 1 cup chips.
Bake until tester inserted into center comes out clean, about 35 minutes. Cool cake in pan on rack.