Prepare the Pan:
Line an 8×8 or 9×9-inch square baking pan with parchment paper, leaving an overhang on two opposite sides for easy lifting later.

Combine and Cook:
In a heavy saucepan, combine granulated sugar, cubed butter, and evaporated milk. Stir constantly over medium heat until butter melts and mixture comes to a full rolling boil.

Cook to Temperature:
Continue boiling and stirring constantly until the mixture reaches 234°F (112°C) on a candy thermometer (soft-ball stage). This takes about 5–7 minutes after boiling starts.

Mix in Chocolate and Marshmallow:
Remove from heat and quickly stir in white chocolate chips until fully melted. Then add the marshmallow crème and stir until completely smooth and uniform.

Divide and Flavor:
Scoop out about 1 cup of the mixture and set aside. To the remaining mixture, stir in orange extract and orange gel food coloring (if using) until fully combined.

Assemble and Swirl:
Pour the orange fudge into the prepared pan. Drop spoonfuls of the reserved white fudge on top and use a knife or toothpick to swirl the two together. Don’t overmix—aim for a marbled effect.

Cool Completely:
Let the fudge cool at room temperature for 3–4 hours until firm, or refrigerate for 2 hours for quicker setting. Bring to room temp before slicing for cleaner cuts.