Preheat the oven to 350 degrees Fahrenheit.

Place sweet potato cubes in a large pot. Just barely cover the sweet potatoes with water. Boil for 15 minutes, or until you can easily pierce with a fork. Drain and mash.

To the mashed sweet potatoes, add butter, eggs, brown sugar, vanilla, pumpkin pie spice, milk and salt. Stir to combine.

Grease a 2.3 quart pan and add sweet potato mixture. Smooth out to make an even surface.

Make the pecan topping. Combine pecans, softened butter, flour and brown sugar and mixture to coat the pecans. Spread it over the top of the sweet potatoes as even as you can.

Bake at 350 degrees Fahrenheit for about 40 minutes, or until you see the pecan topping start to brown.

Remove from the oven.

For marshmallow topping, place marshmallow fluff container in the microwave and microwave on high for 10-20 seconds to soften.

Turn on your oven broiler to high.

Spread the marshmallow fluff across the top of the casserole. Place in the oven on the top rack to toast the marshmallow under the broiler.

This can take anywhere from 20 seconds to 2 minutes. You will need to check it every 10-15 seconds. If you see areas starting to blacken, it's time to take it out! Please keep a careful eye on it.

Serve warm!