Prepare the Pan: Line a 9×13-inch baking dish with foil or parchment paper, leaving a little overhang for easy removal. Lightly butter or spray the lining to prevent sticking.
Combine the Base Ingredients: In a large, heavy-bottomed saucepan, add the butter, sugar, and evaporated milk. Place over medium-low heat and stir constantly as the butter melts and the sugar begins to dissolve.
Boil the Mixture: Once the mixture reaches a full rolling boil, set a timer and boil for exactly 5 minutes, stirring continuously. The mixture should thicken slightly and have a glossy texture — this step is key for achieving that signature creamy consistency.
Add Chocolate and Marshmallow: Remove the pan from the heat. Immediately stir in the chocolate chips, vanilla, and the entire jar of marshmallow crème. Continue stirring until the chocolate chips are fully melted and the mixture is smooth with no streaks of marshmallow remaining.
Optional Add-Ins: If you’re using chopped walnuts or pecans, fold them in at this stage while the fudge is still warm and pliable.
Pour and Set: Quickly pour the hot fudge mixture into the prepared pan, spreading it evenly with a spatula. The fudge will begin to firm up as it cools, so work efficiently.
Cool Completely: Let the fudge cool at room temperature for several hours, or until fully set. For faster results, you can refrigerate it for about an hour, but room temperature yields the creamiest texture.
