Melt butter in a 3-quart saucepan over medium heat. Add green onions and cook 5 minutes, stirring frequently. Add flour; cook 1 minute, stirring constantly. Gradually stir in half-and-half and continue stirring until smooth. Bring to a boil, stirring constantly.
Stir in oyster liquor and TABASCO® Sauce. Cook and stir until soup thickens. Add oysters and parsley; reduce heat to low and continue cooking 5 to 10 minutes longer. Do not boil.
Makes 4 cups.