Heat oven to 350 degrees and position rack in lower third. Combine topping ingredients in a bowl.
Combine filling ingredients in another bowl. Pour filling into a 9-inch pie dish and sprinkle with topping.
Place dish on a parchment-lined baking sheet and bake until bubbling and golden, about 50 minutes. (Tent with foil if becoming too dark.) Let cool slightly and serve topped with Cardamom Custard.