Step 1

Position an oven rack in the center of the oven and preheat to 350 degrees F.

Step 2

Peel, core, and slice apples into 1/4-inch slices. Place apples in a large mixing bowl and toss with sugar, lemon juice, flour, and cinnamon. Pour into a lightly greased 9 by 13-inch baking dish, and spread out into an even layer. Set aside.

Step 3

In another large bowl, mix together the nuts, flour, oats, sugar, cinnamon, and salt for the topping. Using a pastry cutter or your fingers, gently work in the cold butter until pea-sized lumps are formed.

Step 4

Top apples evenly with mixture and bake until apples are bubbly and topping is golden brown, about 45 minutes, rotating once halfway through cooking.

Step 5

Serve warm or at room temperature with vanilla ice cream.