Make the Garlic Parmesan Butter
Mix the butter, parmesan, garlic, parsley and 1/4 tsp of salt together. Season with pepper and extra salt to taste.
1 Stick Butter, 1/2 C Parmesan Cheese, 1 tsp Dried Parsley, Salt and Pepper to Taste, 4-8 Cloves Garlic
You can use it straight away, but I prefer to let this compound butter sit and marry for at least an hour, preferably overnight. If letting it sit for more than two hours, put it in the refrigerator and take it out an hour before cooking to soften. Prep the Sandwich Filling
Mix the leftover spaghetti with the 1 C grated cheese. Once mixed, taste it for salt and pepper. Note: make sure the leftover spaghetti is not hot when you mix the cheese in, or it will melt and make it difficult to stuff the sandwiches. Save the melting for the grilling. 1 C Leftover Spaghetti Marinara or Spaghetti and Meat Sauce, 1 C Mozzarella, Asiago, Provolone Cheese or Italian Cheese Mix
Make the Sandwiches
Note: Make sure your compound butter and spaghetti/cheese mixture are at room temperature before cooking. This will make it easier to melt and crisp everything without burning the bread.
Another Note: Texas toast is thicker and stronger than normal sandwich bread, so it can hold more filling. If Using Texas toast, I recommend making two sandwiches (but you can still spread the filling across three if you like). If using normal sandwich bread, I recommend spreading the filling across three sandwiches.
Heat a nonstick pan or skillet to medium-low heat. Make sure it is nonstick or the parmesan crust will cause a lot of issues.
Spread a layer of the parmesan butter across one side of each piece of bread. Don't worry if you don't use all the butter. Put any extra back in the refrigerator and use it later on a steak or mashed potatoes.
4 to 6 Slices Texas Toast, Sandwich Bread, or Similarly-Sized Garlic Bread
For Each Sandwich:
Put a slice of bread, butter side down, onto the hot pan.
If making three sandwiches, top the bread with a third of the spaghetti/cheese mixture. If making two sandwiches, top with half of the mixture.
Top that mixture with another slice of buttered bread, buttered side up (this way, when you flip the sandwich, the buttered side will be touching the pan).
Let the sandwich grill for 1-2 minutes over medium heat, letting the parmesan crisp up. Then, using a spatula, carefully flip the sandwich. Note: you may have to scrape a little parmesan off the pan. Continue flipping every 1-2 minutes until the center of the sandwich is warm and melty and the outside of the sandwich has a nice golden parmesan crust. Note: flipping every couple minutes will help prevent the outside of the sandwich from burning. Give the sandwich a couple minutes to rest before serving. It goes great with marinara sauce or ranch dressing.
Ranch Dressing or Marinara Sauce for Dipping