Ingredients

1 tablespoon vegetable oil
1 1/2 pounds hanger steak, trimmed
Salt and pepper
2 tablespoons unsalted butter
2 medium yellow onions, thinly sliced (about 5 cups)
2 fresh jalapeño peppers, thinly sliced (see Notes)
2 garlic cloves, thinly sliced
1 tablespoon Worcestershire sauce
2 teaspoons sugar
1/2 cup heavy cream
2 teaspoons apple cider vinegar
4 sturdy rolls, such as ciabatta, halved lengthwise (see Notes)
4 cups loosely packed salad greens (optional)