Begin by preparing your baking dish. Line an 8-inch square baking dish with parchment paper, allowing some overhang for easy removal later.
In a medium saucepan, combine the butter and chocolate chips. Melt over low heat, stirring frequently until smooth and well combined.
Once melted, remove the saucepan from heat and stir in the sweetened condensed milk, mashed bananas, vanilla extract, and salt. Mix until everything is well incorporated.
If you are adding nuts, fold them into the mixture at this point.
Pour the banana fudge mixture into the prepared baking dish and spread it evenly with your silicone spatula or spoon.
Allow the fudge to cool at room temperature for about 15 minutes, then transfer it to the refrigerator for at least 2 hours, or until firm.
Once set, lift the fudge out of the baking dish using the overhanging parchment paper. Cut into 12 squares with a sharp knife.