Line an 8x8-inch baking pan with parchment paper or wax paper for easy removal after chilling. Set aside.
In a medium saucepan over lowheat, melt the butter and white chocolate chips together. Stir occasionally until smooth and combined. Once fully melted, remove from the heat and set aside.
In another saucepan, warm the sweetened condensed milk over low heat. Do not let it boil; simply heat it until it is slightly warm to the touch. This step helps the sugar cookie mix dissolve smoothly.
Gradually whisk in the sugar cookie mix to the warm condensed milk a little at a time, stirring constantly. This ensures the mix dissolves properly without forming lumps. Continue to cook for a minute to ensure the raw flour is fully incorporated.
Switch off the flame and combine all the ingredients. Add the melted butter and white chocolate mixture to the warm condensed milk and sugar cookie mix. Stir everything together until fully combined and smooth.
Stir in the vanilla extract and fold in any sprinkles to add a festive touch to the fudge.
Pour the fudge mixture into the prepared pan, smoothing the top with a spatula. Add more sprinkles on top if desired. Cover the pan with plastic wrap or foil and place it in the refrigerator for 2-3 hours, or until set.
Once the fudge is firm, remove it from the pan using the parchment paper overhang. Use a sharp, warm knife to cut it into 1.5-inch squares or desired pieces. Clean the knife between cuts for smooth edges.
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Notes
You can substitute white chocolate chips with milk or dark chocolate chips for a different flavor profile.
Be sure to warm the condensed milk gently, as overheating it can result in a chewy fudge.
Storage: Store the fudge in an airtight container in the refrigerator for up to 1 week. For longer storage, freeze the fudge as per the instructions in the storage section above.
Customization: You can add other mix-ins like crushed candy canes, nuts, or chocolate chips to make the fudge even more festive or personalized.