For the sweet potato gelato: Preheat the oven to 450 degrees F.
Combine 7 cups water with the granulated sugar, brown sugar, milk, cream and milk powder in a large pot and heat until the mixture is about to boil, about 10 minutes. Watch carefully as it can boil over quickly. Stir in the cinnamon and allspice and let it sit to infuse for 15 minutes.
Scrub the sweet potatoes and split them in half lengthwise. Place on a sheet pan cut-side up. Roast until tender and nicely caramelized, about 1 hour. (Visual cue: when the juices start to ooze they should be taken out.) When cool enough to touch, scoop out the meat with a large spoon, place in a food processor and puree. 4 large sweet potatoes should yield about 5 cups of puree.
Mix the sweet potato puree into the cream base while the mixture is still hot using an immersion blender. Alternatively, use a standard blender. Chill the mixture in the refrigerator for at least 4 hours.
For the pecan praline: Melt the butter in a saucepan over medium heat. Mix in the brown sugar. When the sugar has dissolved, stir in the pecans and salt. Cook for 5 minutes then set aside to cool to 40 degrees F.
To make the sweet potato gelato: Transfer the sweet potato mixture to an ice cream maker and process according to the manufacturer's instructions. When it looks like ¿wet¿ gelato it is ready; this can take as little as 10 minutes. Don¿t let it go too long or it will become dry. Scoop the gelato out of the machine and use a spatula to fold in the pecan praline. Don¿t skimp on the praline. Each bite should have hearty sweet potato combined with rich pecan praline.
When blending hot liquids, first let cool for 5 minutes or so, then transfer to a blender, filling only halfway. Put the lid on, leaving one corner open; this will prevent the vacuum effect that creates heat explosions. Cover the lid with a kitchen towel to catch splatters and pulse until smooth.
This recipe was provided by a chef, restaurant or culinary professional. It has not been tested for home use.