Line an 8x8-inch baking pan with parchment paper, leaving some overhang for easy removal.

Add chocolate chips, sweetened condensed milk, and butter to a medium heatproof bowl.

Place the bowl over a pot of simmering water (double boiler setup).

Stir constantly until the chocolate and butter are fully melted and the mixture is smooth.

Remove the bowl from heat and stir in vanilla extract and salt.

Fold in any optional add-ins like nuts or marshmallows if desired.

Pour the fudge mixture into the prepared pan, spreading it evenly with a spatula.

Sprinkle any desired toppings (e.g., crushed peppermint or sprinkles) over the top.

Refrigerate the pan for at least 2 hours, or until the fudge is firm.

Once set, lift the fudge out of the pan using the parchment paper overhang.

Cut the fudge into squares with a sharp knife, cleaning the blade between cuts for smooth edges.

Store in an airtight container at room temperature for up to 1 week or refrigerate for up to 3 weeks.