Step 1: Line an 8x8 inch baking dish with parchment paper, leaving an overhang on two sides for easy removal.
Step 2: Combine the sweetened condensed milk and chocolate chips in a large microwave-safe bowl.
Step 3: Microwave on high for 1 minute. Stir thoroughly with a sturdy spatula. The chocolate will not be fully melted.
Step 4: Return to the microwave for another 30 seconds. Stir again. Continue heating in 15-second intervals, stirring after each, until the mixture is completely smooth and glossy. (Alternatively, melt in a double boiler over simmering water, stirring constantly).
Step 5: Pour the smooth fudge mixture into the prepared baking dish and spread evenly using the spatula. Gently tap the dish on the counter a few times to settle the fudge and release any air bubbles.
Step 6: Refrigerate for at least 2-4 hours, or until completely firm. For faster setting, you can place it in the freezer for 30-45 minutes.
Step 7: Once firm, use the parchment paper overhangs to lift the fudge out of the pan onto a cutting board. Cut into 1-inch squares with a sharp knife. For cleaner cuts, warm the knife under hot water and wipe dry between slices.
Step 8: Serve immediately or store in an airtight container at room temperature for up to one week, or in the refrigerator for up to two weeks.