Use this crumb topping recipe to make Nectarine Crumb Pie.
In the bowl of a food processor, combine flour, sugar, and cinnamon. Add butter; pulse until large crumbs form, about 30 seconds. (If you don't have a food processor, rub butter into flour mixture with your fingers until large crumbs form.) Add oats; pulse until just combined. Leftover topping can be stored in the freezer for up to 3 months.