1 Preheat oven to 350°F and grease a 9-inch pie pan.
2 In a bowl, combine rolled oats, and ½ cup butter. Knead the crumble until all ingredients are mixed well.
3 Combine sliced apples with sugar, cinnamon and nutmeg.
4 Firmly pat three quarters of the dough into the pan. With finger, spread the dough out into a thin layer. The balance of the dough will be used for the crumble topping.
5 Pour apples on top of the oat crust and then the water. Cut remaining butter into pats and place over the apples. This helps to emulsify the apples when cooking. Add remaining crumble on top of the apples, firmly patting into place. It will not completely cover the apples, but that is fine. Sprinkle walnuts over the crumble and in between the gaps.
6 Bake covered for 50 minutes. Remove the cover and bake an additional 10 minutes.
7 Let cool for 30 minutes before serving.