Boil or roast the sweet potatoes. I roasted mine. FYI, foil isn't necessary. It's just my personal preference.
Preheat the oven. Prepare your filling. You'll need to add all the ingredients in to a bowl and then use whatever appliance you have to make the sweet potato casserole smooth.
Assemble the sweet potato casserole. Grease the pan all over with butter.
Pour the sweet potato filling into a the baking dish. Bake for 20 minutes.
Lastly, take the sweet potato casserole out of the oven. DON'T turn off the oven just yet.
You can leave it as is (without pecans or marshmallows) or make it more decadent by topping it with marshmallows and pecans. Bake until the marshmallows are gooey and golden brown.