Roast Beef with Mushrooms in Wine Sauce

ROAST BEEF WITH MUSHROOMS IN WINE
SAUCE

1 1/2 lbs. rare roast beef, cut into 1/2" strips
1 lb. fresh mushrooms, sliced
3 shallots or 1 sm. red onion, finely chopped
3 tbsp. butter
1/2 c. port or Marsala wine
1/2 tsp. prepared mustard
Salt & fresh ground pepper to taste
1 Baked pastry shell

Heat 1 tablespoon butter in skillet; add shallots and mushrooms and sauté until golden brown. Add beef, wine and increase heat, stir until reduced to half. Add remaining butter and stir quickly into mixture. Serve immediately in warm pastry shell