This is a classic: sweet pastry with apples, a creamy sour-cream custard, and a crunchy crumb topping. Cooking the apples before combining them with the custard prevents them from seeping water into the custard while the pie is baking.
2pounds (900g) Golden Delicious apples, peeled, cored, and sliced
Set a rack on the lowest level of the oven and preheat to 350°F (180°C).
For the filling, place the apples in a large sauté pan with the butter and sugar. Cook over high heat, stirring and tossing, until about half the apples have dissolved, 5 to 7 minutes. Transfer the apple mixture to a bowl to cool.