This recipe makes delicious sammys for laid back weeknights. We recommend using french bread or hoagie rolls from the bakery section of the grocery store as opposed to buns from the bread aisle for sturdier, crustier results. When youre ordering sliced roast beef from the deli counter, ask that its sliced thinly so you can pile it on the sandwiches in delicate easy to chew layers. Low, slow heat is the best way to go when cooking the onions so you end up with a ton of sweet caramelization and no burning.