Heat oil in a large frying pan over medium-high heat. Saute onion until browned, about 5 minutes. Reduce heat and add chane. Mix curry paste with apple juice until smooth, then add to pan. Simmer mixture 10 minutes, stirring occasionally and adding more apple juice or water as needed to keep mixture moist.
Cut each sheet of pastry into 3 equal-size rectangles, then cut each rectangle in half. (You will have 18 pieces total.) Dust a clean, flat surface lightly with flour, and roll each piece of pastry until it is double in size. Dust pastry with flour as needed, to prevent it from sticking to rolling pin. Spoon an equal amount of filling into centre of each pastry square. Fold in half and press edges to seal. Place on nonstick baking trays.
Bake in preheated oven for 25 minutes, until golden brown.