Place bacon on a foil covered bacon sheet and place in a cold oven.Bake bacon at 400 degrees for 20 minutes.Remove bacon, chop finely and set aside.Boil a pot of heavily salted water.In a small pot melt the flour and butter and mix together until it turns into a slightly browned paste (approximately 2 minutes).Slowly whisk in the milk and continue to heat for 5-8 minutes until the sauce thickens to a gravy.Add the salt, nutmeg and truffle oil. Mix together.Add the bacon and mix together (set aside some for decoration).Add the Gruyère and white cheddar cheese, mix together and continue to heat until everything melts together.Boil pasta per boxes instructions and drain. Set aside some of the pasta water before draining.Add pasta to cheese bechamel sauce and mix together well.Add about ¼ cup of the pasta water to the macaroni and cheese to thin out the sauce which should be very thick at this point.Place macaroni and cheese in a small casserole dish and lightly top with panko bread crumbs.Broil for 3-5 minutes until the bread crumbs brown.Finish by crumbling some bacon on top of the dish.