Line an 8x8 inch square baking dish with parchment paper or lightly grease it.

In a microwave-safe bowl, combine 2 cups of chocolate chips, 1 can of sweetened condensed milk, and 2 tablespoons of butter.

Heat in 30-second intervals, stirring after each, until the mixture is completely melted and smooth.

Optional Add-ins: If desired, stir in chopped nuts or vanilla extract.

Pour and spread the fudge mixture evenly into the prepared dish.

Refrigerate for about 2 hours, or until the fudge is firm.

Cut the firm fudge into squares and serve.