For the filling
4 to 5 pounds sweet potatoes (5 to 6 large), roasted and skins removed (See Recipe Notes)
1/4 cup (50 g) granulated sugar
1/4 teaspoon kosher salt
1/2 cup (4 fluid ounces) milk
4 eggs (200 g, weighed out of shell), lightly beaten
5 tablespoons (70 g) unsalted butter, melted and cooled
1/2 teaspoon vanilla extract
For the crumble topping
3/4 cup (105 g) all purpose gluten free flour (I used Better Batter)
Scant 1/2 teaspoon xanthan gum (omit if your blend already contains it)
1/4 cup (25 g) certified gluten free old-fashioned rolled oats (See Recipe Notes)
1/4 cup (55 g) packed light brown sugar
1/4 cup (50 g) granulated sugar
1 1/2 teaspoons ground cinnamon
1/8 teaspoon kosher salt
6 tablespoons (84 g) unsalted butter, melted and cooled
To roast the sweet potatoes
Preheat your oven to 375°F. Wash and dry the raw sweet potatoes, then pierce all over with the tines of a fork. Wrap each separately in aluminum foil, place on a rimmed baking sheet, and bake until a paring knife inserted in the center of the thickest part of each sweet potato doesn’t encounter any resistance (45 minutes to 1 hour+, depending upon size). Remove the sweet potatoes from the oven, unwrap them, and allow them to cool until you’re able to handle them.
Once roasted and skinned, your sweet potatoes should weigh at least 3 1/2 pounds. Keep that mind as you select the number of sweet potatoes you will prepare.
About the gluten free oats
So-called “purity protocol” gluten free oats are safe to eat, but if you avoid them anyway, you can replace the oats in the crumble topping recipe with 1/4 cup (35 g) additional all purpose gluten free flour (for a total of 1 cup (140 g).
About the food processor
If you only have a small food processor, purée the sweet potatoes in batches, and then mix everything together in a large bowl. If you don’t have a food processor, I’ve made the filling with a hand mixer, but it’s just not as smooth.
First, preheat your oven to 375°F and roast the sweet potatoes according to the instructions in the Recipe Notes. As they roast, prepare the topping, which will need to chill.
To make the crumble topping, in a medium-sized bowl, place the flour, xanthan gum, oats, brown sugar, granulated sugar, cinnamon, and salt, and whisk to combine, working out any lumps in the brown sugar. Add the melted butter, and mix to combine well. The mixture will be thick. Place the bowl in the refrigerator to chill for at least 10 minutes or until firm.
Reduce the oven temperature to 350°F. Grease a 9-inch x 12- or 13-inch baking dish and set it aside.
In the bowl of a food processor fitted with the steel blade (See Recipe Notes), place the sweet potato flesh and process for about 2 minutes. With the food processor still working, add the remaining ingredients (granulated sugar, salt, milk, eggs, butter, and vanilla) through the shoot and process until smooth. Stop the food processor as necessary to scrap down the sides and keep the mixture moving. The filling will be thick but very soft and smooth.
Transfer the filling to the prepared baking dish, and smooth the top into an even layer. Remove the crumble topping from the refrigerator, break it up into irregular pieces with the tines of a fork, and sprinkle the pieces evenly over the top of the filling.
Place in the center of the preheated oven and bake until the topping is golden brown and the filling appears set (about 45 minutes). Allow the dish to cool completely before serving.