Line your 9x9 inch pan with parchment paper, leaving some overhang on the sides for easy removal.
In a microwave-safe bowl, combine the chocolate chips, butter, and sweetened condensed milk.
Microwave the mixture in 30-second bursts, stirring well each time, until the mixture is smooth, shiny, and completely melted—about 1-2 minutes total.
Stir in the vanilla extract until fragrant and well combined.
Pour the glossy chocolate mixture into your prepared pan, spreading it evenly with a spatula or the back of a spoon.
Sprinkle a pinch of flaky sea salt or chopped nuts on top if you like a salty crunch or extra flavor contrast.
Gently press down to ensure the mixture is evenly distributed and level at the surface.
Place the pan in the fridge and chill for at least 2 hours until the fudge is firm and set.
Once set, lift the fudge out of the pan using the parchment overhang and transfer to a cutting board.
Use a sharp knife to cut the fudge into squares, wiping the blade clean between cuts for neat edges.
Serve immediately or store in an airtight container in the fridge for up to a week. Let the fudge sit at room temperature for 10 minutes before enjoying for the best melt-in-your-mouth experience.
