Leftovers: Cool completely, then refrigerate in an airtight container up to 4 days. Reheat slices in the microwave for 30–45 seconds or warm in a 350°F (175°C) oven for about 10 minutes. Variations: Swap ground beef for turkey, chicken, pork, or Italian sausage; reduce added salt if using seasoned sausage. Cheese swaps: Cheddar, Monterey Jack, Gruyère, or a blend all work well. Tip: Make sure your skillet is oven-safe (no plastic handle).