2Add the diced sweet potatoes to a large pot and cover with water.
3Boil the sweet potatoes until they are fork-tender.
4Drain the sweet potatoes and let them cool off for a bit.
5Add 1/4 cup of butter, 1/2 cup of brown sugar, 1 teaspoon of cinnamon, 1 teaspoon of nutmeg, 1/2 teaspoon of salt, and 1 teaspoon of vanilla extract to the sweet potatoes.
6Mix all the ingredients together with the sweet potatoes.
7Add 1/2 cup of milk and two eggs to the sweet potato mixture and mix thoroughly.
8Spread half of the sweet potato mixture into the bottom of a 9x13 baking dish.
9In a separate bowl, add 6 tablespoons of butter, 1 tablespoon of cinnamon, 1 cup of flour, and 1 cup of packed brown sugar for the cinnamon filling.
10Mash the cinnamon filling ingredients together with a fork until crumbly.
11Spread 3/4 of the cinnamon filling mixture over the sweet potatoes in the baking dish, reserving 1/4 for later.
12Add the remaining sweet potato mixture on top of the cinnamon filling and smooth it over.
13For the topping, in a bowl, combine 1/4 cup of butter, 2 tablespoons of flour, and 2 tablespoons of brown sugar.
14Use a fork to mash the topping ingredients until crumbly.
15Add 1 cup of chopped pecans to the topping mixture and mix well.
16Spread the pecan topping mixture evenly over the sweet potatoes.
17Add 1 1/2 cups of mini marshmallows over the pecan topping.
18Add the reserved 1/4 of the cinnamon filling on top of the marshmallows.
19Bake the casserole at 350 degrees Fahrenheit for 30 minutes.