Mushroom Croustades
["3 Tbsp. butter", "1/2 lb. mushrooms, finely chopped*", "1/2 tsp. salt", "1/4 c. sour cream", "1 pkg. frozen puff pastry, thawed", "1 large onion, finely chopped*", "1/4 tsp. dried thyme", "2 Tbsp. flour", "1 Tbsp. dry sherry"]
["*I use the Cuisinart."]
["butter", "mushrooms", "salt", "sour cream", "frozen puff pastry", "onion", "thyme", "flour", "sherry"]