Preheat the oven to 250 degrees F. In a skillet, fry the bacon over moderate heat till crisp, drain on paper towels, and crumble finely. Pour 3 tablespoons of the bacon fat into a stove-top popcorn popper or deep, heavy saucepan with a lid, add the oil, and heat over moderately high heat till the mixture begins to smoke. Add the popcorn into a large ovenproof pot, add the cheese, bacon, and salt, and toss. Heat in the oven till the cheese is melted, about 5 minutes. Serve hot.
