Can be made ahead and frozen. I like to freeze the pies before the final bake (sweet potatoes blended and put in the pie dishes, without the nuts, covered tightly with a double layer of saran wrap. I then add the nuts and bake it when I am ready to serve it. (I actually keep large batches of these chopped nuts mixed with maple syrup in my freezer so I can easily add them on at the last minute without the mess.)   Warm up uncovered in the oven or on top of the crock pot/blech.   No need to buy chopped pecans and pay more. Give whole ones a quick pulse in the Vitamix or food processor to get the size pieces you want.