Beef Filet with Mushrooms in Wine Sauce

1½ pounds filet mignon or tenderloin tips, cut into ½-inch strips
1 pound fresh mushrooms, sliced
3 shallots or 1 small red onion, finely chopped
3 Tablespoons butter
½ cup Madeira
½ teaspoon Dijon mustard
Salt and freshly ground pepper to taste
4 frozen puff pastry shells, baked according to package directions

In a large skillet, sauté meat in 1 Tablespoon butter until pink. Remove meat and set aside. Heat 1 Tablespoon butter in skillet; add shallots or onion and mushrooms and sauté until golden brown. Add Madeira. Increase heat and stir until reduced by one-half. Add remaining butter and stir quickly into mixture. Serve immediately in warm pastry shells. Yield: 4 servings.