Mix, bake, serve. Bar cookies are that basic. But here basic means extremely easy, not bland or boring. Brownies (like our delectable Mocha Brownies) fall into this category, and it's hard to imagine a more delicious dessert or one with a bigger fan club. Unlike drop cookies, which use a soft dough, bar cookies are made with a fluid batter that needs a baking pan with sides for support. For best results, spread the batter evenly in the pan, so that the finished bars aren't thin and dried out in one corner and thick and underdone in another. Let the bars cool in the pan, then cut into uniform portions such as squares, rectangles, triangles, or diamonds (see the technique for Making Bar Cookies with a Crust). To remove for storage, first run a sharp, thin-bladed knife between the bars and the inside edge of the pan, then lift them out with a spatula that is large enough to fully support each piece.
If the baking pan must be greased, do it as the first step in the recipe. Coat a piece of paper towel or waxed paper with shortening, then apply in a thin, even layer on the bottom and sides of the pan.
If the batter calls for a melted ingredient such as chocolate, let it cool slightly before beating in the eggs. Then gently stir in the remaining ingredients, such as flour and baking powder, with a wooden spoon.
Spreading Batter in Pan
Spread the batter in a smooth, even layer across the pan bottom with a rubber spatula or the back of a wooden spoon. If the pan has sharp corners, as does this one, make sure the batter fills each one completely.
Testing for Doneness
Toward the end of baking time, begin to check for doneness. Depending on the recipe, look for the batter to be set, for the edges to be slightly browned, or for the mixture to pull away slightly from the sides of the pan.