Bar cookies are one-pan wonders, delicious and simple to make. Join Martha as she prepares four different kinds - peanut butter and jelly bars inspired by everyone's favorite childhood combo, a rich and decadent brownie with a surprise ingredient, pecan bars with a sticky toffee-like topping, and a healthy fruit and nut energy bar. Each is a guaranteed to be a hit with friends and family or at the next bake sale.