Difficulty: Medium - experience needed
6 teaspoons vegetable oil
2 small onions , chopped
1 1/2 pounds sirloin steak tips , pounded until paper-thin
Table salt and ground black pepper
8 thin slices provolone cheese , cut in half
4 (6-inch) sub rolls , slit partially open lengthwise
1. Heat 2 teaspoons oil in large nonstick skillet over medium-high heat until shimmering. Add onions and cook until softened and golden, about 5 minutes. Transfer to small bowl.
2. Heat additional 2 teaspoons oil in now-empty skillet over high heat until smoking. Place half of steak slices in skillet (don't worry if they overlap) and season with salt and pepper. Cook until meat is no longer pink, about 1 minute per side. Remove pan from heat, layer 4 half-slices of cheese over some meat, top with more with meat, and finally 4 more half-slices of cheese. Cover pan with lid to melt cheese, about 1 minute. Divide meat and cheese between 2 rolls, top with half of onions, and pour juices accumulated in skillet over meat. Wrap each sandwich tightly in foil and set aside while preparing remaining sandwiches.
3. Wipe skillet clean with paper towels and repeat step 2 with remaining 2 teaspoons oil, meat, cheese, and onions. Wrap sandwiches in foil and let sit for about 1 minute to let flavors come together. Serve.