Line an 8x8-inch baking pan with parchment paper or aluminum foil. Leave some overhang on the sides to make it easy to lift the fudge out later.
Place the chocolate chips and sweetened condensed milk into a large microwave-safe mixing bowl. Heat the mixture in the microwave on full power in 30-second intervals. After each interval, stir well to ensure even heating. Continue this process until the chocolate is fully melted and the mixture is smooth and uniform in color.
Once melted and combined, pour the mixture into the prepared pan. Use a spatula to spread it evenly, smoothing out the top.
Place the pan in the refrigerator and let the fudge set for at least 2 hours, or until firm. For faster results, you can chill it in the freezer for about 30-40 minutes.
Once the fudge has set, lift it out of the pan using the parchment or foil overhang. Place it on a cutting board and cut it into squares or rectangles.