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Export 7 ingredients for grocery delivery
Step 1
Heat oil in a large skillet over medium heat. Add onions and cook for about 10 minutes or until softened, stirring frequently. Transfer to a plate and set aside.
Step 2
Cut the leftover steak into thin slices.
Step 3
Lightly butter the bread and toast until golden.
Step 4
Top the bottom half of bread with arugula and caramelized onions.
Step 5
Place a layer of the thin steak slices on top, and spread mustard on top.
Step 6
Season with optional salt and pepper if necessary.
Step 7
Cover the sandwiches with the top half of the bread.