Line baking pan with parchment paper and leave an overhang so you can pull the fudge out easily. Don’t skip this or the fudge will be tough to remove. Cut the butter into tablespoon-sized pieces.
Add butter, chocolate chips, salt, and sweetened condensed milk to a heavy-bottomed nonstick pot. Set the heat to the lowest setting and stir constantly with a heat-safe spatula, scraping the bottom and sides as you go. Keep the heat low the whole time.
Once the mixture is mostly melted, remove from heat and stir until totally smooth. Stir in the vanilla.
Pour the mixture into your lined pan. Lightly spray a spatula with cooking spray and smooth the top. If desired, sprinkle the top with miniature chocolate chips and gently press them into the top. Cover and refrigerate 3–5 hours or until fully set.
Lift the fudge out using the parchment overhang. Cut into small pieces with a hot, sharp knife (run under hot water, wipe dry, and cut quickly). It’s rich, so smaller squares work best.
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Notes
Note 1: Good chocolate makes a big difference. I love Ghirardelli and Guittard (not sponsored). Use milk chocolate, dark chocolate, or a mix — I usually go half milk, half dark.Storage: Keep leftover fudge in an airtight container in the fridge for 1–2 weeks, but it’s best within the first couple of days. If it sits out too long or pieces aren't individually wrapped well, it starts to dry out.Freezing: Cut the fudge into squares and wrap each piece tightly in plastic wrap. Place the wrapped pieces in a large freezer bag and press out as much air as you can. If you skip wrapping them individually, separate the squares with wax paper so they don’t stick together. Thaw in the fridge.