Caramelize onions by slicing your onion into thin slices and cooking it slowly in a heavy bottom sauté pan (or dutch oven) on a low heat until they are dark brown. I drizzle a little oil in the pan first, then as the onion is cooking add a splash of balsamic vinegar and a sprinkle of sugar to help bring out the flavor. This takes about 30 minutes, but can be done up to 24 hours in advance.
Assemble the sandwich by first placing one slice of havarti cheese on each piece of bread.
Top one slice the havarti for each sandwich with 2 oz of cambozola.
Top the cambozola with your caramelized onions.
Top onions with 2 slices of bacon.
Melt 4 T butter in a large skillet and let it melt.
Place sandwiches in the melted butter and cook until brown.
Flip sandwich and cook until melted and brown on the other side.