Combine sugar, butter, salt and cream in a large saucepan. After it reaches a boil, stir continuously for four minutes.

Remove from heat. Stir in white chocolate and marshmallow cream. Stir continuously until mixture is completely combined.

Pour about half of the mixture into a parchment paper lined 13x9 baking dish.

Add root beer concentrate to remaining mixture. Stir until combined. Pour over white fudge. Using a knife, swirl the two together. (you need to do this quickly, before the white fudge has time to set up)

Put fudge in a refrigerator for a minimum of 3 hours. Cut into pieces and serve!