Preheat oven to 190ºC (375ºF). Peel, core and dice apples; toss with lemon juice.
Melt butter in large skillet over medium heat. Stir in diced apples, sugar, cinnamon and nutmeg; cook about 5 min. to begin softening apple. Sprinkle flour overtop. Stir through; cook another 5 min., or until apple is tender. Spoon filling into four 4-in. (10-cm) ramekins (1 cup/250 mL).
Tip pie shell out of foil dish onto lightly floured work surface. Pat pastry flat, patching together any large cracks. Using a 4-in. (10-cm) round cutter (or dish to trace), cut out 4 pastry rounds. Cut a small "X" in the centre of each round for air vent. Use tines of fork to crimp edges. Whisk together egg and 1 tbsp (15 mL) water. Brush pastry with egg wash and sprinkle with sugar. Place pastry rounds on top of warm apple filling.
Bake about 15 min., or until crusts are golden brown and filling is bubbling. Let stand a few minutes before serving. Serve with ice cream or whipped cream, if desired.
Re-roll pastry scraps, wrap and freeze for future use.