Halve, peel, and thinly slice the onion. Slice the Brie into 1/8 inch thick pieces.

In a small pan over medium heat, heat one tbsp butter. Add onions to pan and cook until caramelized, about 6 minutes.

If using prosciutto: preheat oven to 350. Add a thin layer of olive oil to a sheet pan. Lay the pieces of prosciutto out on the pan and bake for about 5 minutes or until lightly crispy. If using bacon: cut the bacon into small strips and sauté over medium heat until crispy, about 7-8 minutes. Drain excess grease on a paper towel.

Spread two pieces of bread with fig jam. Layer the cheese (about 3-4 inch wide slices per sandwich each) over the jam. Spread the bacon or prosciutto evenly across the cheese. Top each side of the sandwich with the caramelized onions and the other piece of bread.

Heat 1 more tbsp butter in a pan over medium heat. Add the sandwiches, cooking each side in the butter until cheese is melty and the bread is lightly browned to your liking. Flip and repeat on the opposite side.