Adapted from Deelish Dish
3/4 cup all-purpose flour
1/4 cup packed light brown sugar
1/2 cup plus 2 tablespoons granulated sugar
8 tablespoons butter, cold, cut into small cubes (1 stick)
1 cup old-fashioned rolled oats (not quick oats)
6-7 apples peeled, cored, and cut into 1/2 inch chunks
juice of one lemon
1 tablespoon ground cinnamon
1 dash of nutmeg
Preheat oven to 375 degrees F. In a large bowl, mix together flour, brown sugar, and 2 tablespoons granulated sugar. Cut butter into flour with two knives until mixture is the texture of coarse meal. Add oats and use your hands to toss and squeeze mixture until large, moist clumps form. Transfer to freezer to chill while you prepare apples.
In another large bowl, toss apples with lemon juice, cinnamon, nutmeg, and remaining 1/2 cup granulated sugar. (note: if using granny smith apples, add an extra tablespoon or two of sugar) Transfer to a 9 x 12 baking dish and sprinkle with topping mixture. Place baking dish on a rimmed baking sheet and baked until golden brown and bubbling, 55 to 65 minutes. Cool before serving. Serve with ice cream, heavy cream or milk.