In large skillet, melt 1 tbsp (15 mL) of the butter over medium heat; cook onion for about 5 minutes or until lightly browned.  Add 1-1/2 tsp (7 mL) of the curry powder; cook for 30 seconds. Add apple, apple juice, currants, salt and pepper; cook until liquid evaporates, about 5 minutes.

Trim ends of squash and cut into 4 thick slices or rings; remove seeds. Set aside. 

In small skillet, melt remaining butter over medium heat; stir in remaining 1 tsp (5 mL) curry powder and stir until fragrant.  Brush some over 13- x 9-inch (3 L) baking dish.  Arrange squash rings in single layer.  Spoon apple filling into centre of rings; drizzle with remaining curry butter (mostly on squash). Cover with foil and bake in 350°F (180°C) oven until squash is tender, 45 to 50 minutes. Remove from pan using lifter. Serve sprinkled with coriander, if desired.