Beef Fillets with Stilton-Portobello Sauce

6 (6-ounce) beef tenderloin fillets
2 teaspoons chopped fresh tarragon
1/2 teaspoon freshly ground pepper
5 tablespoons butter or margarine, divided
8 ounces portobello mushroom caps, sliced
1/3 cup dry red wine or beef broth
1/2 cup sour cream
3 ounces Stilton or blue cheese, crumbled and divided
Garnish: fresh tarragon sprigs

1. Rub fillets with tarragon and pepper.
2. Melt 2 tablespoons butter in a large skillet
over medium-high heat.
Cook fillets 4 to 5 minutes on each side or to desired
degree of doneness.
Remove from skillet, and keep warm.
3. Melt remaining 3 tablespoons butter in skillet.
Add mushrooms,
and saut'e 3 to 4 minutes or until tender.
Add wine (or beef broth),
and cook 1 to 2 minutes,
stirring to loosen particles from bottom of skillet.
Stir in sour cream.
Sprinkle 1/4 cup cheese into sauce, stirring until melted.
4. Arrange fillets on a serving platter, drizzle with sauce.
Sprinkle with remaining cheese, and garnish, if desired.
Makes 6 servings.