1/2 cup (65 grams) all purpose flour
1/4 cup (50 grams) granulated white sugar
1/4 cup (55 grams) light brown sugar
1/2 teaspoon ground cinnamon
1/4 teaspoon fresh or ground nutmeg (optional)
1/8 teaspoon salt
6 tablespoons (84 grams) cold unsalted butter, cut into pieces
1/3 cup (30 grams) old-fashioned rolled oats
1/3 cup (40 grams) chopped walnuts or pecans
6 cups (1.2L) Granny Smith Apples or other firm, tart-tasting apple (peeled, cored, and cut into 1 inch (2.5 cm) chunks)
1 cup (240 ml) fresh blackberries or raspberries (optional)
Juice of 1/2 lemon
1 teaspoon lemon zest
3 tablespoons (40 grams) white granulated sugar
Preheat oven to 375 degrees F (190 degrees C) and place rack in the center of the oven. Butter or spray with a non-stick cooking spray, a 9 inch (23 cm) deep dish pie plate or an 8 x 8 x 2 inch (20 x 20 x 5 cm) baking dish. (Can also make eight individual ramekins.)
Topping: Place all the topping ingredients (flour, sugars, spices, butter, oats, and nuts) in a food processor and process until the mixture is crumbly (looks like coarse meal) and there are no large pieces of butter visible. (This can also be done with two knives or your fingertips.) Set aside while you prepare the filling.
Filling: Place the apple chunks in a large bowl, along with the berries (if using) and lemon zest. Toss with the lemon juice and sugar. Transfer to your prepared baking dish. Spread the topping evenly over the apples.
Bake for approximately 30-40 minutes (20- 25 minutes for individual ramekins) or until bubbly and the topping is golden brown. (If you insert the tip of a sharp knife into a chunk of apple, it should be tender, not mushy.) Remove from oven and place on a wire rack to cool for about 30 minutes before serving.
Serve with softly whipped cream or vanilla ice cream. Refrigerate leftovers and reheat before serving.