Drain canned sweet potatoes well and place in a bowl.
Mash sweet potatoes and mix with remaining casserole ingredients until smooth.
Spread into a 2-quart baking dish.
Mix together marshmallows, pecans and butter. Sprinkle over the mashed sweet potatoes.
Bake for 20 minutes or until heated through. Cool 5 minutes before serving.
Notes
Drain the sweet potatoes very well for the best flavor and consistency.
Make the casserole ahead of time and reheat! Bake without the topping, cool and then refrigerate overnight. Simply sprinkle the topping on and bake until heated and the marshmallows become toasted.
Refrigerate leftovers covered for up to 4 days. Reheat covered with foil in the oven.
Freeze this casserole, covered with plastic wrap, for up to 6 months. Thaw in the refrigerator before reheating.
For a different flavor profile, make a streusel topping instead! Mix a cup of flour, ¾ cup brown sugar, and ¼ cup salted butter, and mix until crumbly. Spread on top of sweet potato mixture and bake.