Preheat the oven to 350 degrees. Line baking sheet with parchment paper.
Place the washed sweet potatoes on the baking sheet. Bake for 90-120 minutes until the potatoes are soft and cooked through.
Allow the potatoes to cool until they can be handled. Scoop out the sweet potatoes into a large bowl. Stir in melted butter, milk, sugar, vanilla, and salt. Taste and adjust the salt if needed.
Stir in the eggs until the casserole is mixed thoroughly.
Pour into a 9x13 baking dish.
In a separate bowl, make the topping. Mix together the brown sugar, gluten-free flour, pecan pieces and melted butter.
Sprinkle the topping over the top of the casserole.
Bake for 60 minutes until the top begins to brown and it pulls away from the pan on the sides.
Serve.