Directions

1. Preheat oven to 450 degrees. Place sweet potatoes on a baking sheet, and roast until very soft, about 1 hour. Allow to cool. Peel off skin, and discard. Place sweet potatoes in the bowl of a food processor, and puree until completely smooth. Measure 1 1/2 cups puree, reserving any excess for another use. This step may be done a day in advance.
2. Reduce oven to 325 degrees. Combine 1 cup sugar and the water in a small saucepan, and cook over medium heat. Cook, stirring occasionally, until sugar dissolves. Brush down sides of pan with a pastry brush dipped in water to prevent crystallization. Increase heat to medium-high; boil, without stirring, until the syrup turns a deep amber, 5 to 6 minutes. Pour caramel into savarin mold or a 9-by-2-inch round cake pan. Holding the pan with pot holders, swirl to coat bottom and halfway up sides of dish.
3. In a large bowl, combine sweet-potato puree, remaining 3/4 cup sugar, allspice, cinnamon, salt, eggs, and egg yolks. Mix in vanilla and scalded milk, then pass the mixture through a fine sieve. Pour into caramel-lined pan, and cover with foil. Set in a roasting pan, and pour boiling water into the roasting pan halfway up sides of flan dish.
4. Bake for 50 to 55 minutes, or until center of flan is nearly set: A thin-bladed knife inserted in the center should come out clean. Let cool to room temperature, and place in the refrigerator to chill overnight.
5. To unmold, run a sharp knife carefully around flan, and cover with a serving plate; invert quickly. Remove pan; serve.