Heat oven to 350. Line a 9" x 13" pan w/ foil, spray foil w/ cooking spray. In bowl, beat butter until creamy. Beat in brown sugar and eggs. Beat in 2 cups peanut butter and 2 tsp vanilla. Measure out 2 cups and set aside.
Press remaining mix into bottom of pan. In microwave bowl, microwave condensed milk, 1-1/2 cups chocolate chips and 2 tbsp peanut butter until melted. Stir in 2 tsp vanilla.
Spread mix over dough in pan. Crumble reserved dough over chocolate mix in pan. Sprinkle w/ remaining chocolate chips. Bake 30 mins. Let cool, cut into bars.