How to Make It
Combine beef, 2 1/4 teaspoons oil, Worcestershire, 1/2 teaspoon salt, and 1/2 teaspoon pepper in a bowl; mix with hands. Divide into 4 portions, shaping each into a 4-inch patty.
Heat a skillet over medium-high heat. Add 1 tablespoon oil to pan. Add patties to pan; cook 3 minutes on each side. Remove patties from pan. Add remaining 1 tablespoon oil to pan; swirl to coat. Add onion and mushrooms to pan; cook 6 minutes or until mushrooms brown. Sprinkle with flour, remaining 1/4 teaspoon salt, and remaining 1/4 teaspoon pepper; cook 2 minutes. Add stock to pan; cook 1 minute or until thickened and slightly reduced, stirring frequently. Return patties to pan, and spoon onion mixture over patties. Sprinkle evenly with cheese. Cover; cook 3 minutes or until cheese melts.