Grilled Ham and Cheese Sandwiches with Caramelized Onions

I like to put at least one sandwich on the menu each week. They're usually easy to make and we all enjoy them (although Baby Girl likes to deconstruct her sandwiches/burgers so she can eat each ingredient separately. Don't ask.) I saw these Hot Ham and Cheese Sandwiches with Bacon and Caramelized Onions on Pinch of Yum and thought they'd make a great grilled cheese sandwich.

I asked SP to get a loaf of rye bread at the store and it was the perfect bread for these sandwiches. Even though everything is better with bacon, I ended up skipping the bacon on these since they already had ham. The caramelized onions added just the right amount of sweetness to cut through the savory sauce. Delicious.

Grilled Ham and Cheese Sandwiches with Caramelized Onions
Modified from Pinch of Yum

1 yellow onion
1 tablespoon butter
1/4 cup mayo
2 teaspoons Dijon mustard
1 teaspoon Worcestershire sauce
spreadable butter
8 slices of bread (I used rye)
1 pound sliced deli ham
1/2 pound sliced Swiss cheese

Slice the onion into thin strips. Melt 1 tablespoon butter in a small skillet; add onions and cook over very low heat for 30 minutes, stirring occasionally. The onions will turn a deep golden color.

Whisk the mayo, mustard and Worcestershire sauce together.

Spread some of the spreadable butter on each slice of bread. Flip each slice over and spread 1/4 of the sauce on each of four slices, then top those slices with 1/4 of the ham, onions, and cheese. Complete the sandwiches with the other four slices of bread to make four sandwiches, butter side out.

Heat a griddle over medium-low heat. Add the sandwiches and cook until the bread is golden brown on both sides and the cheese melts. You want to go low and slow so the cheese and filling have a chance to warm through before the bread burns.

Cut in half and serve immediately.