In a medium microwave safe mixing bowl, combine chocolate chips and sweetened condensed milk.
Microwave for 30 seconds, stir, and repeat, microwaving in 30-second increments until chocolate is melted and ingredients are fully combined (about 2 minutes)*
Pour fudge mixture into the prepared pan. Evenly spread with a silicone spatula, tapping the pan lightly on the counter to flatten.
Refrigerate for 4 hours or until the fudge is set.
Use a sharp knife to slice the fudge into 1-inch pieces.
Store in an airtight container in the refrigerator, or in a cool, dry spot for up to 1 week.
Notes
*Do not overheat or the fudge will stiffen and be unworkable.
The chips should be just melted. Make sure fudge is thoroughly chilled and set before slicing.
Use a very sharp knife, and if necessary, dip in hot water and wipe in between slices.