In a 12 inch skillet cook chicken in hot oil over medium-high heat for 4 - 5 minutes or till no longer pink. Remove chicken; set aside. Add garlic, mushrooms and onion to skillet. Cook, uncovered, for 4 - 5 minutes or till liquid evaporates.
In a bowl stir together sour cream, flour, 1/2 teaspoon salt and 1/4 teaspoon pepper. Add sour cream mixture, milk, and broth to skillet. Cook and stir until bubbly. Cook 1 minute more. Add chicken and Madeira or sherry; heat through. Serve over Herbed Biscuits. Sprinkle with thinly sliced green onions if desired. Makes 6 servings. Herbed Biscuits: In a mixing bowl stir together 1 3/4 cup packaged biscuit mix, 2 Tablespoons thinly sliced green onion, and 1/2 teaspoon crushed, dried oregano. Add 1/2 cup skim milk; stir just until dough clings together. On a floured surface knead dough 10 to 12 strokes. Roll to a 1/2 inch thickness. Using a 2-inch biscuit cutter, cut dough into 12 biscuits.
Reroll the trimmings as necessary. Bake biscuits on an ungreased baking sheet in a 425 degree oven for about 12 minutes.