Season Schweid & Sons The Prime Burger* patties with salt and pepper.
*The Prime Burger is 100% USDA prime chuck
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.
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.
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.
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).