Line a 9 x 9-inch baking pan with foil.
Combine sugar, brown sugar, evaporated milk, pumpkin, butter and pumpkin spice in a saucepan.
Bring to a boil over medium heat, stirring constantly. Continue boiling, stirring constantly, for until a candy thermometer reaches 234°F (soft-ball stage), about 10-12 minutes.
Remove from heat and quickly stir in white chocolate, marshmallow crème, nuts, vanilla, and salt.
Stir vigorously for 1 minute or until chocolate is melted and marshmallow crème is thoroughly combined.
Immediately pour into prepared pan.
Cool on wire rack until completely cooled (room temperature), about 2 hours.
Tightly cover and refrigerate until set.
To cut, lift from pan; remove foil. Cut into 1-inch pieces. Makes about 3 pounds.