Heat oven to 400 degrees. Place unopened pea pouch in warm water for 10 to 15 minutes to thaw. In large skillet, brown ground beef with onion and garlic; drain. Stir in sour cream, flour, thyme and pepper until well blended. Fold in thawed peas. Pour mixture into 1 1/2 quart shallow casserole. Cut pastry sheet to fit inside top of casserole. Place on top of ground beef mixture. Brush lightly with beaten egg. Prick pastry with fork in several places to allow steam to escape during baking. Bake at 400 degrees for 25 to 35 minutes. Makes 4 servings.