These Amazing Patty Melt Sandwiches combine juicy seasoned beef patties, caramelized onions, melty Muenster and cheddar cheese, and a creamy homemade sauce. Everything is layered between buttery slices of sourdough or rye bread and grilled until golden and crisp. They are a hearty, comforting sandwich that is perfect for lunch or an easy dinner.
In a bowl, mix the sauce ingredients. Refrigerate until ready to assemble the sandwiches.
For the caramelized onions, melt the 2 Tbsp of butter in a skillet. Add the onions and 1/2 tsp sugar. Cook over medium-low heat, stirring occasionally, for 10-15 minutes, until the onions have caramelized.
In a bowl, mix the ground beef with the salt, pepper, and Worcestershire sauce together. Shape into 3 patties. Cook in a skillet over medium heat until both sides are browned and the patties are cooked all the way through.
Butter the outside of all 6 bread slices. Assemble the sandwiches by placing 1 slice of bread, butter side down. Spread some of the sauce over the bread. Then top with a slice of Munster and cheddar. Then place the patty on the bread along with some of the caramelized onions. Finish by spreading some sauce on the unbuttered side of another slice of bread. Then place butter side up on the sandwich. Grill in the skillet until both sides are browned. Make the other 2 sandwiches the same way. Makes 3 sandwiches.