Saute sausage in 10-in. skillet over medium-high heat until meat to render fat, about 5 minutes. Break up sausage with back of wooden spoon. Stir in leeks and thyme and reduce heat to medium. Cook covered until leeks are golden and soft, about 15 minutes. Heat oven to 400° Unfold 1 pastry sheet on ungreased baking sheet. Spread half the sausage mixture lengthwise over half of pastry, leaving 2-in. border at long edge. Beat egg and milk lightly together and brush over 2-in. border. Fold pastry over and press border with fingertips. Trim border with sharp knife. Brush top with egg wash. Cut slits in top 1/2 in. apart and parallel to short edges. Repeat with second sheet pastry and remaining sausage mixture. Bake until lightly browned and puffed, about 20 minutes. Cut into 1-in. slices and serve hot. Serves 8. Nutritional value: 370 cal, 7 g prot, 26 g fat, 27 g carb, 446 mg sod