→ Apples
01 - 6 medium tart apples (such as Granny Smith), peeled, cored, and sliced
02 - 2 tablespoons lemon juice
→ Sugar & Spices
03 - ½ cup granulated sugar
04 - 1 teaspoon ground cinnamon
05 - ¼ teaspoon ground nutmeg
→ Crumble Topping
06 - 1 cup all-purpose flour
07 - ¾ cup rolled oats
08 - ½ cup packed light brown sugar
09 - ½ teaspoon salt
10 - ½ cup unsalted butter, cold and cut into cubes
→ Optional
11 - ½ cup chopped walnuts or pecans