Line an 8-inch x 8-inch square pan with parchment paper. Set aside.
Place a medium saucepan over medium-low heat. Add the butter and heat until melted. Then stir in the sugar, half and half, chocolate chips, marshmallow fluff, vanilla, and food coloring. Cook until melted, combined, and smooth.
Pour the fudge mixture into the prepared pan. Refrigerate until set, about 2-3 hours.
If you would like to add a drizzle on top, do so once the fudge is set. You can either add cream cheese frosting or white chocolate chips to a bowl. Microwave for 10-30 seconds at a time, stirring between each heating, until it reaches a thin consistency. Drizzle the topping over the pan of fudge.
Once the fudge is set, use the parchment paper to lift it from the pan. Then, cut the block into a 4x4 grid to yield 16 pieces of fudge.
Notes
You can use an 8x8-inch pan or a 9x9-inch pan. The larger pan will make the fudge slightly less thick.
You can cut the fudge into a 5x5 grid (25 pieces) or a 6x6 grid (36 pieces) if preferred. Nutritional information will vary accordingly.