Place semisweet chocolate chips, red velvet emulsion, 1 oz cream cheese, 1 ½ tsp vanilla and ½ tsp cream of tartar in a heat safe bowl and set aside.
13 ½ ounce semisweet chocolate chips, ¼ cup red velvet emulsion, 3 ounce cream cheese, 2 ½ teaspoon vanilla, 1 teaspoon cream of tartar
Place white chocolate chips, 2 oz cream cheese, 1 tsp vanilla, 1 tsp cream cheese emulsion and ½ tsp cream of tartar in another heat safe bowl and set aside.
3 ounce cream cheese, 2 ½ teaspoon vanilla, 13 ½ ounce white chocolate chips, 1 teaspoon cream cheese emulsion
In a large, heavy saucepan over medium heat combine sugar, butter, marshmallows, half & half and salt. Stirring frequently, cook the mixture to 238° - 243° F.
4 ½ cup sugar, 2 ¼ sticks butter, 10 ounce mini marshmallows, 1 cup half & half, ¾ teaspoon salt
Immediately scrape half of the mixture into the bowl with the semisweet chocolate chips and half of the mixture into the bowl with the white chocolate chips.
Using an electric mixer, mix until smooth, starting with the bowl containing the white chocolate and then moving to the bowl containing the semisweet chocolate.
Using two spoons/scoops, place alternating scoops of red and white fudge in the prepared pan until all of the fudge has been added to the pan.
Drop pan from a few inches above counter a couple times to remove any air pockets and level the fudge.
With a knife, swirl through the fudge to give a marbleized appearance.
Allow to cool completely before cutting into squares and storing in an airtight container.
Notes
If you want a brighter red color, use red food coloring rather than the red velvet emulsion.