1. Season Schweid & Sons The Prime Burger* patties with salt and pepper.
2. Heat 2 tbsp. oil in a skillet over medium-high heat. Season the sliced onions with salt and pepper, and saute until softened and browned, stirring occasionally, about 12 minutes. Transfer the onions to a bowl.
3. Add more oil to the skillet and heat over high heat. Cook Burger patties, flipping once each, until well browned, about 4 minutes total. (Work in batches as necessary). Transfer patties to a plate.
4. Top each of 4 potato bread slices with some of the onions, a cheese slice, and a Burger patty. Top each Burger with a cheese slice and another piece of potato bread. Using a table knife, spread butter over the top and bottom of each sandwich.
5. Heat a nonstick skillet over medium heat. Cook each sandwich, flipping once, until golden-brown and hot, about 6 minutes. (Work in batches as necessary).