Since I grew up in the Chicago area, my family ate Italian beef sandwiches every now and again. When I asked my mom for her recipe, she told me that she just simmered roast beef and a container of au jus on the stovetop, and put it on big, crusty rolls. Au jus is simply the juice from roasting beef, and she can find it in the deli section of her local grocery store. Here in the South, though, I have never seen au jus for sale; I had to start from scratch.