Crab St. Jacques

1/2 cup butter or margarine, divided
2 tablespoons flour
1/2 teaspoon salt
1 cup light cream
1/2 pound mushrooms, sliced
1 medium onion, minced
2 tablespoons parsley
8 ounces to 1 pound frozen or fresh lump crabmeat
3 tablespoons sherry

In a small saucepan, blend 1/4 cup melted butter with flour and salt. Stir in cream gradually. Cook, stirring constantly, over medium heat until thick and smooth. In another pan, saut