Prepare an 8" x 8" square pan by lining it with foil, then lightly coat the foil with a nonstick spray.
Place the milk chocolate chips in a medium size glass, microwave-safe bowl. Pour the sweetened condensed milk over the chips, and stir to coat.
Microwave on high for 1 minute. Stir to combine; it should be a very smooth consistency. If the chocolate chips aren't completely melted, give them a few more seconds in the microwave, and stir again.
Pour the fudge mixture into the prepared pan. Smooth top as much as possible. Let the fudge cool until set. Sprinkle with a little finishing salt, if desired.