Line an 8×8 inch square pan with parchment paper, leaving an inch or two overhang on all sides.
Melt the butter in an sauce pan over medium heat.
Add the white sugar, evaporated milk, corn syrup, pumpkin puree and pumpkin pie spice to the melted butter in the sauce pan. Stir with a wooden spoon to combine.
Cook over medium-high heat, stirring constantly until the soft balled stage is reached. Soft ball stage is reached when the mixture has reached 234 degrees Fahrenheit. Check the temperature frequently with a candy or an instant thermometer.
Once the mixture has reached 234 degrees remove the pot from the heat and add the white chocolate chips, the marshmallow fluff and the vanilla extract to the saucepan. Stir the fudge ingredients together with a wooden spoon to mix in the marshmallow fluff and to melt the white chocolate chips.
Stir until there are no streaks and the vanilla chips are melted. Work quickly or the fudge will stiffen and be difficult to spread into the 8 x 8 pan.
Carefully scoop the fudge into the prepared pan and smooth the top as much as possible with the back of your spoon.
Allow the fudge to cool and set up for at least 4 hours or overnight is best, before cutting.
Once the fudge is complexly cooled it will be firm enough to cut into perfect one inch squares. Lift the fudge from the pan by the edges of the parchment paper. Place the pumpkin fudge down on a table or counter. Use a large sharp knife to cut the fudge into 1 inch squares.
Store in an airtight container. Fudge can be packaged and shipped and makes a great holiday gift.