Page 157 - My Cookbook

It goes in a pan under the meat in the oven during roasting. I love it (but not as much as I love mine and I hope she doesn't read this).
3) While the meat is roasting (mmmmm, smells sooooo good), cut the bell peppers in half and remove the stems and seeds. Rinse, and cut into 1/4" strips. Cook the peppers in a frying pan over a medium high heat with enough olive oil to coat the bottom, about 1 tablespoon. When they are getting limp and the skins begin to brown, about 15 minutes, they are done. Set aside at room temp.
4) Remove the roast and the juice pan. Take the meat off the rack and remove the rack. Pour off the juice, put the meat back in the pan, and place it in the coldest part of the refrigerator. Let it cool for a few hours, long enough for the meat to firm up. This will make slicing easier. Chill the juice, too, in a separate container. Slice the meat against the grain as thin as humanly possible, preferably with a meat slicer. My wife remembers that her family would cook the roast and take it to the butcher to slice on his machine. That's a good strategy if you don't have a meat slicer but it may be against your local health codes. If you don't have a slicer, use a thin blade and draw it along the meat. If you try to cut down or saw through the crust you will be cutting it too thick.
5) Taste the juice. If you want you can thin it with more water, or make it richer by cooking it down on top of the stove. In Chicago beef stands it is rich, but not too concentrated. Then turn the heat to a gentle simmer. Soak the meat in the juice for about 1 minute at a low simmer. That's all. That warms the meat and makes it very wet. You can't leave the meat in the juice for more than 10 minutes or else it starts to curl up, squeezes out its natural moisture, and toughens. If you go to a beef stand and the meat is really curly, they have committed a mortal sin. At Mr. Beef, for example, I watched them take a handful of cooked beef and dump it into the juice every time they took out enough for a sandwich. This also enriches the juice with meat protein and seasoning from the crust.
6) To assemble the sandwich, start by spooning some juice directly onto the bun. Get it wet. Then lay on the beef generously. Spoon on more juice (don't burn your hand). Top it with bell pepper and, if you wish, giardiniera. If you want it "wet", dip the whole shootin' match in juice. Be sure to have plenty of napkins on hand.
Variations on the theme
Da Combo. Most Italian beef joints offer a "combo," which also has a grilled Italian sausage nestled in with the beef (shown being made at Al's in a photo at right). These are thick, uncured, coarsely ground pork sausages in natural casings, flavored with fennel, paprika, black pepper, red or green bell peppers, onions, garlic, parsley, and crushed red chili peppers for some heat. Italian sausages are made in your choice of hot, medium, or mild (sometimes called sweet).
Da Cheef. Cover it with shredded mozzarella and/or provolone, broil for a few minutes, and you have a "cheesy beef" or "cheef". Not many stands offer this mutant strain.
Wit Gravy. An even rarer and more heretical variant, topped with marinara.
Da Soaker. Just dip the bread in the juice and you have the classic laborer's lunch, a soaker, a.k.a. "sugo pane", or gravy bread. Sugo pane is also commonly made with marinara sauce.