Line an 8x8-inch baking pan with parchment paper, letting some hang over the sides to create handles. Lightly spray the parchment with nonstick spray to make it easier to lift out and slice the fudge later.
In a large microwave-safe bowl, add the white chocolate chips, sweetened condensed milk, and butter pieces. Use a silicone spatula to gently stir so the chips are coated in the condensed milk for more even melting.
3 cups white chocolate chips, 14 oz sweetened condensed milk, 3 tablespoons unsalted butter
Microwave the mixture on 50–60% power for 30 seconds, then stir well. Continue microwaving in 20–30 second bursts at reduced power, stirring after each burst, until the mixture is mostly melted and smooth. A few small soft lumps are fine; they will melt as you stir.
3 cups white chocolate chips, 14 oz sweetened condensed milk, 3 tablespoons unsalted butter
Quickly stir in the cotton candy flavoring, vanilla extract, and pinch of fine sea salt. Taste a tiny bit carefully (it will be warm) and add up to an additional 1/4–1/2 teaspoon cotton candy flavoring if you want a stronger flavor, keeping in mind it will mellow slightly as it chills.
1 teaspoon cotton candy flavoring or extract, 1 teaspoon vanilla extract, 1 pinch fine sea salt
Working fairly quickly while the mixture is still warm, divide the fudge base evenly between two medium bowls. Add a drop or two of pink gel food coloring to one bowl and blue gel food coloring to the other. Stir each until the color is fully blended, adding more coloring a drop at a time until you reach your desired pastel shade.
pink gel food coloring, blue gel food coloring
Spoon large dollops of pink and blue fudge into the prepared pan, alternating colors in a rough checkerboard pattern. Once all the fudge is in the pan, use a butter knife or wooden skewer to gently swirl the colors together. Avoid over-swirling so you keep distinct pink and blue ribbons.
While the top is still soft, scatter cotton candy sprinkles or pastel rainbow sprinkles evenly over the surface. Gently press them into the fudge with your fingertips so they adhere. Do not add loose cotton candy yet, as it will melt in the fridge.
3-4 tablespoons cotton candy sprinkles or pastel rainbow sprinkles
Cover the pan lightly with plastic wrap or foil and refrigerate for at least 2 hours, or until the fudge is firm enough to slice. For very clean squares, chill 3–4 hours or overnight.
Use the parchment handles to lift the fudge out of the pan onto a cutting board. With a sharp knife, cut into 1-inch squares or your preferred size, wiping the blade with a warm, damp cloth between cuts for neat edges. If desired, top each piece with a small tuft of loose cotton candy just before serving.
loose cotton candy