Step 1

In a medium bowl, whisk together the flour, brown sugar, sugar, cinnamon, nutmeg, and salt. Grate the cold butter into the bowl. Cut in the butter using a pastry blender or two knives, until the pieces are no larger than pea sized. Add the walnuts and toss to combine.

Step 2

Spray the crock pot with cooking spray, then add the apple slices to the crock pot. Add the sugar, corn starch, cinnamon, and lemon juice, and toss to combine.

Step 3

Sprinkle the topping in an even layer over the apples. Cover and cook on high for 2 hours, or on low for 4 hours. Partially uncover, and continue cooking for one hour to remove the excess moisture from the topping. Serve warm with ice cream or whipped cream on top.