It's actually really easy if you use the right bread. A boule loaf is necessary, because it's hearty, circular and has a heavy bottom crust. Use your knife to cut thick slices of bread, but leave the bottom inch of the crust uncut. Then, rotate the loaf 90 degrees and cut through the bread again. This will leave a crossed pattern that will pull apart really easily. Don't forget to stuff it with garlic butter and cheese!