Preheat the oven to 250 to 300 degrees F. Lay bread slices on a baking sheet in a single layer. Bake for about 15 minutes, turn the slices over, and bake for an additional 15 minutes. The bread should be perfectly crisp when you remove it from the oven. It should snap when you break up the pieces of bread. Place bread into either a mixer or a blender, and process until the bread crumbs have an even, fine texture. You