Preheat the oven to 375 degrees . Arrange 8 slices bacon on a broiler pan and bake until crisp, 12 to 15 minutes. finely chop the remaining bacon.
In a skillet, heat a drizzle of EVOO over medium-high heat. Add the butter to melt. Add the onion; season with salt and pepper. Cook until softened, about 15 minutes. Add the cider, maple syrup and worcestershire and simmer at a rapic but controlled buble, stirring frequently, for 8 to 10 minutes.
In a bowl, combine the beef, chopped bacon, mustard and lots of pepper. Form into 4 patties thinner at the center than at the edges for even cooking. Drizzle with EVOO and season with salt. Preheat a cast-iron skillet over medium-high heat. Add the burgers and cook for 5 minutes on the first side. Flip and cook for 3 to 4 minutes on the other side for meium doneness. In the last minuet or so, top each burger with 2 slices of cheese to melt.
Serve the burgers on the buns, each topped with 2 slices of crisp bacon and some of the maple onions.