Prepare a 9x9 inch baking dish by lining it with parchment paper.
In a saucepan over low heat, combine the butter, sweetened condensed milk, and chocolate chips.
Stir continuously until the mixture is smooth and fully melted.
Remove from heat and stir in the vanilla extract and salt.
Pour the fudge mixture into the prepared baking dish and spread it evenly.
Sprinkle any desired toppings on top.
Let the fudge cool at room temperature for about 2 hours.
Once set, cut into small squares.
Store the fudge in an airtight container to maintain freshness.