Grind garlic, pepper, salt and chipotle powder in a mortar and pestle or molcajete until it forms a paste. Heat oven to 350°. Remove the top of the sourdough and scoop out the bread leaving about 1/4” in the bottom and sides. Rub the garlic paste into the bread and put it into the oven (lid on the side) for 5 minutes.
Cook 4-5 slices of bacon and set aside (reserving grease). Thinly slice the onion and add to reserved bacon grease. Cook over medium heat until caramelized.
Line the lightly toasted bread with about 4 slices of fontina cheese (chop the rest). Put the bread back into the oven until the cheese is melted (about 3 minutes).
Layer the roast beef into the bottom of the bread. Add the onions and then top with the turkey. Press to remove air. Put the “sandwich” back into the oven and turn it off.
Cook the remaining bacon. Drain on paper towels reserving grease. Add flour to grease and stir until it is lightly toasted. Stir in the buttermilk and stir over medium low heat until absorbed. Stir in the cream and season with salt and pepper to taste. Cook and stir until smooth. Add chopped cheese and stir until the cheese is melted.
Remove the “sandwich” from the oven. Spoon the cheese gravy over the top. Top with chopped bacon and sprinkle with paprika and chipotle powder.