1. In a large mixing bowl, cream the butter, sugar, and peanut butter until creamy.
2. Add the eggs and vanilla and cream again. Sift together the baking powder, salt, and flour. Slowly add to the butter mixture until just mixed in.Stir in the chocolate chips and Reese pieces by hand.
3. Spread half the batter in a greased 9 x13 pan. Drop the marshmallow cream on top. Gently spread across the top. Drop the rest of the batter on top of the fluff and carefully spread out the dough. You may need to use a damp finger or hand to do this.
4. Bake at 350* for 25-28 minutes.
5. Let cool before cutting into bars. Store in a closed container for up to 5 days.