Prepare an 8x8 square dish by spraying it with non-stick spray and lining it with parchment paper, leaving an overhang on both sides. Set it aside.

Place condensed milk and chocolate chips or chopped chocolate into a microwave-safe bowl.

Heat the mixture in the microwave, stirring every 30 seconds, until it is melted and smooth.

Pour the vanilla extract and mix it in.

Pour the fudge mixture into the 8x8 square dish or any other box pan you have. It may be thick and not spread to the corners but don't worry. Simply use the bottom of a spoon or rubber spatula to smooth it down on top, making it as even as possible. If desired, you can add flaky sea salt, chocolate sprinkles, or other ingredients from the fudge variations section.

Place in the freezer until it solidifies.

Once the fudge has hardened, remove it from the pan by lifting the parchment paper and proceed to cut it into equal squares and serve immediately.

Store the rest in the refrigerator or freezer. Take it out 30 minutes before serving and leave it at room temperature. This will guarantee the best texture.