To make a crumb crust for a bar cookie, combine the sugar, butter, vanilla, and salt, and stir until the mixture is well blended. Add flour to the sugar mixture, and stir until blended. The mixture will be crumbly. Firmly press this mixture into the bottom of a greased 8-inch square baking pan. Use your fingers to press the mixture evenly into the pan to make sure that it’s compact. It needs to be compact so that it will hold together when it’s cut. Bake this crust layer for 15 minutes or the time specified in the recipe.
While the crust is baking, combine the mixture for the top layer. Remove the crust from the oven, and pour the mixture over the crust. Our recipe for Two-Layer Caramel Bars calls for sprinkling the topping mixture with pecans, then baking for 3 more minutes. Cool the bars completely on a wire rack. Use a pizza cutter to cut the cookies into 4 equal strips. Remove the strips from the pan, and then cut each strip crosswise into 5 pieces.