Spread batter in prepared baking pan. Drop peanut butter in spoonfuls over the surface of the batter and use a knife to swirl in and create a marbled effect.
Bake 18 to 22 minutes, or until surface of brownies is just barely firm to the touch.
Remove and let cool, then cut into squares.
*You may find that much of the butter and peanut butter bubbles up and is on the surface of the brownies when you remove them from the oven. It will reabsorb as the brownies cool.Serves 16. Each brownie has 5.6 g of carbs and 2.1 g of fiber. Total NET CARBS = 3.5 g.