Lightly coat an 8-inch square glass baking dish with coconut oil cooking spray.
In a medium saucepan over low heat, stir together chocolate chips, sweetened condensed milk, and salt. Stir constantly to avoid burning the chocolate.
Once chocolate is fully melted and ingredients are thoroughly incorporated, remove pan from heat.
Add vanilla extract and (if desired) the nuts, and stir until combined.
Pour fudge mixture into the baking dish, spreading it evenly.
Chill the fudge for 2 hours.
Cut the fudge into 30 squares and serve.