A jelly roll pan is a cookie sheet or baking sheet that has a raised edge. Our recipe calls for a 10.5 x 15.5 inch pan. If you don’t have the specific size of pan, bake these bars in a 9x13 inch pan. The bars will be thicker and require a longer baking time. If baking in a 9x13 inch pan, check the bars at 25 minutes and adjust the baking time as needed.