Use leftover grilled steak to make these sandwiches. You can buy caramelized onions in jars from food shops or you can make your own; they keep well. I keep them on hand to make life easier.

3 tablespoons olive oil

1 Spanish onion, thinly sliced

2 tablespoons sherry vinegar

Salt and freshly ground pepper

1/4 cup Dijon mustard

2 tablespoons horseradish

1 baguette

1 cup shredded arugula

500 grams (about 1 pound) leftover steak or rare roast beef

Heat 2 tablespoons oil in a skillet over medium heat. Add onions and cook for about 10 minutes or until golden and soft. Pour in sherry vinegar, bring to boil and reduce until vinegar disappears. Season with salt and pepper and reserve.

Combine Dijon mustard and horseradish in a bowl. Set aside.

Cut a baguette into 4 portions and cut each portion in half. Brush with remaining olive oil and grill lightly on each side for about 2 minutes per side.

Brush bread with horseradish mustard, add caramelized onions, arugula and beef. Press down and serve.