To prevent bar cookies from crumbling, always cool them in the pan before cutting.
Placing a slice of bread in the cookie jar can soften cookies that are too hard; change the slice every other day. A bread
slice will also keep soft cookies soft, just as it softens hardened brown sugar.
If the recipe says to preheat the oven, allow at least 10 minutes for it to reach the correct baking temperature. Also,
check your oven temperature with an oven thermometer. To do this, place the thermometer in the center of the oven. If the
temperature in the oven doesn't match the one on the oven dial, you may need to adjust your oven dial to compensate for a
too-hot or too-cool oven.
To prevent cookies from becoming hard and tough, avoid adding more flour than necessary to the cookie dough or batter.
Also, avoid overmixing once the flour is added. For even baking, be sure to shape cookies to roughly the same thickness. If
you have a problem with your cookies being too brown on the bottom, avoid dark-colored cookie sheets. Instead, use heavy-gauge
metal cookie sheets with a dull finish (aluminum is ideal).
To test bar cookies for doneness, insert a toothpick into the center of the pan; it should come out clean (unless the
recipe specifies otherwise). Other cookies are done when they're firm at the edges.
If your cookies seem to spread too much when you bake them you may be greasing the cookie sheet when the recipe doesn't
call for it or your cookie sheet may be too warm.
To avoid overcooking, check cookies at the minimum baking time suggested in the recipe, and then watch them closely during
their last few minutes in the oven. Also, after baking be sure to remove small cookies from cookie sheet to wire rack right
away because they'll continue to bake on the hot sheet.
When baking cookies in batches, cool the cookie sheet to room temperature before placing more cookies on it. (You can
do this quickly by running the bottom of the sheet under cool water for a few seconds.) A hot cookie sheet will melt the dough.
If the recipe calls for greasing the sheet, regrease for each batch.