Combine the stock and garlic in a medium saucepan. Bring to a boil over medium-high heat, remove from the heat, and set aside. Melt 1/2 stick of the butter in a small skillet over medium heat. Stir in the flour and cook for about 30 seconds, until blended. Stir the butter and flour mixture into the stock. Return the saucepan to the stove top over medium heat. Stir in the remaining 2 1/2 sticks butter, then the Worcestershire sauce and salt. Stirring constantly, cook until the sauce begins to thicken, about 5 minutes. Serve hot over hot fish.
