• Add sweet potatoes to a large pot filled with water. Bring to a boil over high heat and then reduce heat to medium and simmer potatoes until fork tender, about 20 minutes. Drain well and return to hot pot (off of heat) to allow any extra moisture to cook away.
  3 pounds sweet potatoes
• Preheat oven to 350°F. Spray a 2 quart or 9×13 baking dish with nonstick cooking spray and set aside.

Prepare the Filling

• In a large bowl or the pot the sweet potatoes cooked in, mash the potatoes and softened butter using a potato masher or hand mixer. (You should have about 5 cups of mashed sweet potatoes at this point.)
  6 tablespoons unsalted butter
• Add the remaining ingredients (brown sugar, eggs, half and half, ground cinnamon, vanilla extract and salt) and mash together until your desired consistency is achieved. I like some texture to mine but you can make yours completely smooth if you want.
  ½ cup brown sugar,2 eggs,½ cup half and half,½ teaspoon ground cinnamon,1 teaspoon vanilla extract,½ teaspoon kosher salt
• Evenly spread the filling into the prepared baking dish and set aside.

Prepare Streusel Topping

• In a medium bowl, whisk together the flour, brown sugar, salt, and ground cinnamon. Add the pecans and melted butter and stir together until pecans are evenly coated with the mixture.
  ⅔ cup all purpose flour,⅔ cup brown sugar,½ teaspoon kosher salt,1 teaspoon ground cinnamon,2 cups pecans,6 tablespoons unsalted butter
• Spread the streusel evenly on top of the sweet potatoes.
• Bake the casserole for 25 to 35 minutes or until golden brown on top. Remove from the oven and let cool for a few minutes before serving. If using marshmallows, sprinkle over the top of the casserole with about 15 minutes remaining and cook until they are just golden brown.
  1 to 2 cups miniature marshmallows