Prepare the Pan
Line an 8x8-inch baking dish with parchment paper or foil, leaving a bit of overhang for easy removal. Lightly grease the lining to prevent sticking.
Melt the Ingredients
In a microwave-safe bowl, combine the chocolate chips, sweetened condensed milk, and butter.
Microwave on high in 30-second intervals, stirring after each interval, until the mixture is completely melted and smooth (approximately 2-3 minutes).
Add Vanilla and Nuts
Stir in the vanilla extract and chopped nuts, if using. Mix until evenly incorporated.
Pour and Set
Pour the fudge mixture into the prepared pan, spreading it evenly with a spatula.
Gently tap the pan on the counter to remove any air bubbles.
Chill
Refrigerate the fudge for at least 2 hours, or until firm.
Slice and Serve
Once set, lift the fudge out of the pan using the parchment paper or foil.
Cut into small squares and serve.