Prepare an 8x8 inch (20x20 cm) square pan by spraying it lightly with nonstick cooking spray. Line the pan with a sheet of parchment paper, leaving an overhang on the sides for easy removal of the fudge later.

In a large, microwave-safe bowl, combine the chocolate chips and the sweetened condensed milk.

Place the bowl in the microwave and heat in 30-second increments. After each 30-second interval, remove the bowl and stir the mixture thoroughly. Continue microwaving and stirring until the chocolate chips are completely melted and the mixture is smooth and well combined (this typically takes about 3-4 minutes total).

Pour the hot chocolate mixture into the prepared pan. Use a rubber spatula to spread the fudge evenly into all corners of the pan, smoothing the top surface.

Place the pan in the refrigerator for 2-3 hours, or until the fudge is completely set and firm to the touch.

Once set, use the parchment paper overhang to lift the fudge out of the pan. Place it on a cutting board and cut it into small squares or desired shapes.