Combine 1/2 cup sugar and 1/4 cup water in a small, heavy saucepan over medium heat; cook until sugar dissolves, stirring frequently. Continue cooking until golden (about 4 minutes). Immediately pour into 6 (6-ounce) ramekins or custard cups coated with cooking spray, tilting each cup quickly until caramelized sugar coats bottom of cup. Set aside.
Beat brown sugar, syrup, and eggs in a medium bowl with a whisk. Add pumpkin and next 5 ingredients (pumpkin through evaporated milk), stirring until well-blended. Divide mixture evenly among prepared custard cups. Place cups in a 13 x 9-inch baking pan; add hot water to pan to a depth of 1 inch. Bake at 325° for 1 hour and 10 minutes or until a knife inserted in center comes out clean. Remove cups from pan. Cover and chill at least 4 hours.
Loosen edges of custards with a knife or rubber spatula. Place a dessert plate, upside down, on top of each cup; invert onto plates. Drizzle any remaining caramelized syrup over custards. Garnish with freshly grated nutmeg, if desired.