Pick a bar cookie recipe and follow the steps below.
Some recipes call for a greased pan to make removing the bars easier. Read your recipe carefully; if it calls for a greased pan, use a paper towel to rub shortening over the inside of the pan, coating it completely.
You can also line your pan with foil. This makes it very easy to remove the bars from the pan after they have cooled. If a recipe calls for a greased pan, you will want to grease the foil once it is in the pan.
To line a pan with foil, tear off a piece of foil that is larger than the pan. Turn the pan upside down and shape the foil over the outside bottom of the pan. If necessary, cut slits at the corners so the foil lies smoothly. Lift the foil liner off the pan. Turn the pan over and fit the foil liner into the pan. Set the pan aside while you mix the crust.
Many bar cookies have two or more layers. The first layer is a crust that supports the top layer or layers. Mix the crust ingredients according to recipe directions.
After the crust ingredients are combined, pat the mixture firmly and evenly into the pan. The crust layer must be even so it bakes correctly and the filling layer on top can be even.
Most bar cookie crusts are baked in a 350-degree F oven for about 20 minutes. Check the crust after the minimum baking time; it can burn quickly. The crust is done when the edges are golden brown. Do not overbake or the crust will be too hard.
While the crust is baking, prepare the second layer or filling. Pour this layer over the hot crust. Use a spatula to spread the filling layer evenly, if necessary.
Return the pan to the 350-degree F oven and bake about 20 minutes. When the time is up, open the oven and jiggle the pan gently to see if the center is set. If not, bake for a few minutes more. Once the center is set (doesn't jiggle), let the bars cool in the pan on a wire rack.
Once the bars are cool, if you used a foil liner, you can lift the entire batch from the pan and place it on a cutting board. Use a long, sharp knife to cut into bars. If you didn't use foil, cut the bars directly in the pan and use a spatula to remove them.
Most bar cookie recipes direct you to cut the bars into rectangles or squares of a certain size. Of course, you can cut them any way you wish. For parties, guests will appreciate smaller pieces that are less messy and can be eaten in one bite. Or you may want to wow guests with jumbo-size bars for dessert. Another option is to try triangles or diamonds instead of rectangles.
To make triangles: Cut bars into 2- or 2-1/2-inch squares. Cut each square diagonally in half to make two triangles. Or cut the bars into rectangles and cut the rectangles into triangles.
To make diamonds: First cut parallel lines 1 to 1-1/2 inches apart down the length of the pan. Then cut diagonal lines 1 to 1-1/2 inches apart across the pan, forming a diamond pattern.
Store any leftover bars that contain raw eggs or dairy in a covered container in the refrigerator.