Add cubed sweet potatoes to a large pot of boiling water and allow them to cook until soft. The potatoes should be fork tender, this will make them easier to mash. Once finished cooking, drain the potatoes.
Preheat oven to 375°F and lightly grease a 9x13” casserole dish. Set aside.
In a large bowl (or in the pot the potatoes were cooked in), mash the sweet potatoes with everything except for the pecans and marshmallows.
Then, fold in the pecans and spread everything evenly into the prepared casserole dish. Sprinkle with half of the marshmallows, then make your streusel.
Prepare the streusel by whisking together the brown sugar and flour in a small bowl.
Cut in the butter with forks or by hand, then add in the pecans.
Sprinkle all over the top of the casserole dish, then add the remaining marshmallows.
Bake for 20 minutes or until marshmallows are golden brown and potatoes are heated through.TIP - if you prefer the topping to be a little crispier and caramelized, simply pop the finished casserole under the broiler quickly, around 1 to 2 minutes.
I would suggest sticking to raw sweet potatoes as opposed to canned for this recipe.
You can certainly leave the pecans out if desired. Mini marshmallows bring the entire dish together! However, if you prefer your sweet potato casserole without marshmallows then you're welcome to omit them.