Tiny French Dip

Name: French Dip Sandwich
Yield: 0
Cuisine: french
Ingredients: 1-inch piece boneless ribeye loin; Salt and pepper; 1 tiny onion, sliced; 1/4 teaspoon butter, divided; 1/4 teaspoon chopped garlic; 1 teaspoon onion soup mix; 1 tablespoon beef stock; 1 teaspoon sherry; Dash Worcestershire; 1 teaspoon water; 1 sub roll