Step 1

In a large pan, render the diced bacon over medium heat until it becomes crispy and releases its fat. This will take about 8-10 minutes. Once the bacon is cooked, remove it from the pan and strain it to drain excess fat. Save the bacon fat in a separate container; you'll need it again.

Step 2

In the same pan, add the butter, bacon fat, and chopped onions. Cook the onions over medium heat until they become soft and translucent, stirring occasionally. This will take approximately 5-7 minutes.

Step 3

Pour in the red wine vinegar and continue cooking for another 2 minutes, allowing the vinegar to infuse with the onions.

Step 4

Add the brown sugar to the pan and stir until it dissolves completely.

Step 5

Return the cooked bacon to the pan with the onions and mix everything together.

Step 6

Pour in the water and bring the mixture to a simmer. Reduce the heat to low and let it cook for about 30 minutes or until the liquid thickens and becomes syrupy. Stir occasionally to avoid burning.

Step 7

While the bacon jam is simmering, prepare the sandwiches. Spread a thin layer of mayonnaise on one side of each bread slice.

Step 8

Take another clean pan and place it over medium-low heat. You can also use a griddle if you have one.

Step 9

Assemble the sandwiches: On the non-mayo side of four bread slices, spread a generous amount of the homemade bacon jam. Sprinkle the mozzarella cheddar cheese mix over the jam, and then top each with the remaining four bread slices, mayo side up.

Step 10

Carefully transfer the assembled sandwiches to the heated pan or griddle. Cook each side for 3-4 minutes or until the bread turns golden brown and the cheese is melted.

Step 11

Once the sandwiches are done, remove them from the pan and let them cool for a minute or two.

Step 12

Cut the grilled cheese sandwiches in half and serve them warm. Enjoy the gooey goodness of the bacon jam and cheese combination!