Lay prosciutto or bacon slices in a cold pan and turn on to medium heat. Cook until starting to crisp on one side, flip, and cook until crispy on the other side. Remove from pan and place on a paper towel lined plate.
Without wiping out the pan, sauté shallots in bacon fat and season with salt, stirring occasionally until starting to brown and crisp up. If pan seems dry, add olive oil. Once lightly browned, remove from the pan and put onto a paper towel lined plate. Wipe out the pan.
Spread a thin layer of mayo across one side of each slice of bread. Spread a thin layer of fig jam on the opposite side of 2 pieces of bread.
Heat pan to medium heat. Place a slice of bread, mayo side down and jam side up, into the pan and build the sandwich in the pan by topping with half the cheeses (letting it spill off the side which will create perfectly crispy cheesy edges), shallots, and crispy prosciutto. Top with another piece of jam-less bread, mayo side up, pressing down lightly with a spatula.
Cook 5 to 7 minutes until the bread touching the pan is golden brown. Carefully flip the sandwich. Cover the pan top with tin foil to allow the sandwich to steam slightly and melt the cheese, and top the tin foil with a heavy plate or another pan in order to gently press the sandwich for 3 minutes. For the final 2 minutes of cooking, remove the heavy plate and tin foil. Once the sandwich is golden brown, remove from the pan and repeat with the other sandwich. Wait 3 minutes before cutting at a diagonal.
Makes two sandwiches