Wash and peel the sweet potatoes
Cut them into even chunks
Boil in salted water until fork-tender
Drain well
Mash until smooth
Add butter
Add brown sugar
Add milk or cream
Add eggs if the casserole recipe calls for them
Add vanilla extract
Add cinnamon or nutmeg if desired
Mix until fully combined
Spread into a greased casserole dish
Top with marshmallows, pecans, or a crumb topping if desired
Bake until hot and set