Line an 8×8-inch baking pan with parchment paper, leaving a slight overhang on the sides. This will allow you to easily lift the fudge out once it has set. Lightly grease the parchment with a tiny bit of butter or non-stick spray if desired.
In a large microwave-safe bowl, combine the white chocolate chips and the sweetened condensed milk. Heat in the microwave in 30-second intervals, stirring well after each burst, until the chocolate is completely melted and the mixture is smooth. Alternatively, use a double boiler on the stove over low heat.
Once the mixture is smooth, remove it from the heat. Stir in the vanilla extract, salt, and orange zest (if using). The salt is essential as it balances the sweetness of the white chocolate.
Gently fold in the dried cranberries using a spatula. Ensure they are evenly distributed throughout the thick fudge mixture so every bite has a bit of fruit.
Pour the mixture into your prepared pan and spread it into an even layer using an offset spatula. Smooth the top as much as possible. Place the pan in the refrigerator for at least 2 to 3 hours, or until the fudge is firm to the touch.
Once fully set, lift the fudge out of the pan using the parchment paper edges. Place it on a cutting board and use a sharp knife to slice it into small squares. For the cleanest cuts, dip your knife in hot water and wipe it dry between slices.