Piroshki
["1 (10 oz.) pkg. frozen puff pastry shells", "2 Tbsp. butter", "1/4 c. finely chopped onion", "3 Tbsp. sour cream", "1 1/2 c. chopped cooked beef shank meat", "1/2 tsp. dried dill", "salt and pepper to taste", "1 egg yolk, beaten with 1 Tbsp. water"]
["Remove pastry shells from package and let stand at room temperature to thaw 30 minutes."]
["frozen puff pastry shells", "butter", "onion", "sour cream", "meat", "dill", "salt", "egg yolk"]