This scrumptious bar is a perfect blend of fruit and crumb. Serve it with a dollop of whipped cream if you like. You can try any of your favorite preserves as a filling; you can't go wrong!
Preheat oven to 350 degrees. To make the crust: In a large bowl, combine the butter with the flour until you get a doughlike consistency. Spread crust evenly into an ungreased 12- by 18-inch jelly roll pan. Use a large piece of waxed paper to firmly and evenly press down crust. Bake the crust for 15 minutes. Remove from oven and let cool completely, 30 to 40 minutes.
While the crust is cooling, prepare the topping: Mix the flour and the brown sugar. Using a pastry blender, cut in the butter until the mixture resembles coarse crumbs. When the crust is cool, gently and evenly spread the raspberry preserves over the crust, leaving a 1/4-inch edge all around. Sprinkle crumbs generously over the preserves (it will seem like more than you think you need).
Bake for an additional 15-18 minutes until golden brown. Allow to cool to room temperature, or overnight, before cutting and serving. Makes 24 3-inch squares.