1/4 cup butter
1 large onion, finely diced
1 (16 ounce) can mushrooms, drained and thinly sliced
1/3 cup all-purpose flour
2 1/2 cups chicken stock
1 (15 ounce) can condensed cream of asparagus soup
3 tablespoons dry sherry
3 1/2 cups diced cooked chicken breast meat
36 frozen puff pastry shells, thawed

1. Preheat oven to 400 degrees F (200 degrees C).
2. In a large skillet, melt butter over low heat. Stir in onions and mushrooms, and saute until onions are soft. Stir in the flour and continue to cook for 4 minutes, stirring constantly.
3. Pour in stock gradually, and continue to stir over a medium heat until thickened. Stir in condensed asparagus soup, sherry, and chicken. Reduce heat to low, and simmer until the chicken is done and the sauce has thickened, about 10 minutes.
4. Meanwhile, arrange pastry shells on a 10x15-inch baking sheet. Bake in preheated oven until golden brown, about 8 to 10 minutes. Allow to cool slightly before spooning equal amounts of the chicken filling into each shell. Serve immediately.