Recipe: Hawaiian Roll Party Sliders

Name: Recipe: Hawaiian Roll Party Sliders
Ingredients: 2 tablespoons unsalted butter, divided; 2 large sweet onions (such as Vidalia), thinly sliced; 1/2 teaspoon kosher salt; 2 teaspoons Worcestershire sauce; 1 (12-ounce) package Hawaiian sweet dinner rolls, such as King’s; 12 thin slices deli roast beef (about 12 ounces); 8 ounces Gruyère cheese, grated; 1/2 teaspoon garlic powder; 1/2 teaspoon onion powder; 1 tablespoon finely chopped fresh parsley leaves, for garnish (optional)