This is like pumpkin pie you can hold in your hand! I make a quadruple batch of this and pour it onto 2 very large baking sheets and it makes a lot of fudge. The recipe below is for a regular size batch.
Peheat oven to 350 degrees. Spread walnuts out onto a baking sheet and place in oven for 5-7 minutes until fragrant. Halfway through use a spatula to move the nuts around and turn over so they will toast evenly. Remove from oven and set aside to cool completely.
Line a 13x9 inch baking pan with foil allowing the foil to extend up the two short sides of the pan and overhang both ends slightly. You will use these as handles to lift the fudge out of the pan once it's set.
In a heavy sauce pan, combine sugars, half and half, pumpkin, butter and spices. Bring to a full rolling boil over medium heat, stirring constantly. Continue to stir and boil for 10-12 minutes or until a candy thermometer reaches the soft ball stage at 234-240 degrees F.
Stir in white chocolate chips and keep stirring until chips are completely melted. Add marshmallow creme, 3/4 cup of walnuts and vanilla. Work quickly to stir and thoroughly combine all ingredients. There should be no streaks of white from the marshmallow creme.
Immediately pour into the prepared pan and top with remaining 1/4 cup chopped walnuts. Cool completely before cutting. When ready to cut lift fudge out of the pan using the foil handles you made, discard foil and cut fudge into bite size pieces about 1 inch.