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Spray an 8-inch square baking dish with cooking spray. Line the bottom with parchment paper, spray the paper, and set pan aside.
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Place the white chocolate chips in a large microwave-safe bowl and heat in 15-second intervals, stirring well after each interval, until melted and smooth.
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Remove the lid and foil top from the tub of frosting and heat until pourable, about 30 seconds.
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Pour the frosting over the melted chips, then add the peppermint extract, salt, and food coloring. Stir to combine.
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Quickly add the mini chocolate and stir just 2 or 3 times—you want the chips to melt and create swirls in the fudge; if you stir too much your fudge will be brown rather than swirled.
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Pour the mixture into the prepared baking dish and smooth the top.
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Refrigerate for 2 hours, or until set. Slice and serve.