Step 1: Line an 8×8-inch baking pan with parchment paper, leaving a slight overhang on two sides for easy removal.
Step 2: In a heavy-bottomed saucepan, combine the sugar, butter, and evaporated milk over medium heat.
Step 3: Bring the mixture to a full rolling boil, stirring constantly to prevent burning.
Step 4: Continue boiling for exactly 5 minutes, stirring frequently.
Step 5: Remove from heat and immediately stir in the pumpkin puree and pumpkin pie spice until well combined.
Step 6: Add the white chocolate chips, marshmallow creme, and vanilla extract. Stir vigorously until the chocolate is completely melted and the mixture is smooth.
Step 7: Pour the mixture into the prepared pan and smooth the top with a spatula.
Step 8: Allow the fudge to cool to room temperature, then refrigerate for at least 3 hours (or overnight) until firm.
Step 9: Use the parchment paper to lift the fudge from the pan and cut into 1-inch squares.