Accompaniment : Ice-cream Pre-heat oven to 425 degrees. Peel apple, halve lengthwise, and core. Using a 1-cup ramekin (3 1/4 inches across and 2 1/4 inches deep) as a guide, cut out 2 rounds from pastry sheet. In a 7-inch heavy skillet heat butter over moderate heat until foam subsides and stir in brown sugar and water. Add apples halves and cook, turning frequently, 3 minutes. In 2 (1-cup) ramekins set on a baking sheet arrange apple, cored sides up, and top evenly with sauce. Top apples with pastry rounds, letting edges of pastry hang over sides of apples. Bake tarts in middle of oven for 20 minutes, or until pastry is puffed and golden brown, and cool on a rack 5 minutes. Working with 1 ramekin at a time, invert a plate over each ramekin and invert ramekin onto plate. Carefully lift off ramekins.