1. Preheat oven to 350°.
2. Place sugar and 1/4 cup water in a medium, heavy saucepan over medium-low heat; cook until sugar dissolves, stirring gently as needed to dissolve sugar evenly. Continue cooking 7 minutes or until golden (do not stir). Immediately pour into a 9-inch round cake pan coated with cooking spray.
3. Place pumpkin, pumpkin pie spice, vanilla, eggs, and milks in a food processor; process until smooth. Pour milk mixture over caramel in pan. Place pan in a 13 x 9-inch metal baking pan; add enough hot water to large pan to come halfway up sides of cake pan.
4. Bake at 350° for 1 hour and 10 minutes or until center is set. Remove cake pan from water; cool completely on a wire rack. Cover and refrigerate overnight.
5. Loosen edges of flan with a knife or rubber spatula. Place a large serving plate, upside down, on top of cake pan; invert flan onto plate. Drizzle any remaining caramelized syrup over flan.