Yes, this sweet potato casserole can be made in advance, at least in part. You can make the sweet potato filling with the streusel topping assembled in a casserole dish up to 3 days in advance if kept in the refrigerator, or up to 3 months ahead of time if you keep it in the freezer!u003cbr/u003eu003cbr/u003eu003cstrongu003eFor the refrigerator:u003c/strongu003e Cover the dish in plastic wrap, then get it out on the day and heat for 35-40 minutes (rather than the normal 25-30) until heated through and the streusel topping is beginning to brown a bit. Finish with the marshmallows and broil as per the instructions.u003cbr/u003eu003cbr/u003eu003cstrongu003eFor the freezer: u003c/strongu003eIt's best to use a foil baking dish as they freeze well and can also go in the oven. Simply assemble the sweet potato filling with streusel layer into a foil baking dish, cover completely and freeze it for up to 3 months. Let it fully defrost in the fridge overnight, then follow the instructions for making it from the fridge.