Line a 9x13" baking pan with parchment paper so it comes up the sides of the pan, making it easy to remove the fudge. Set aside.
Combine the chocolate chips, sweetened condensed milk and butter in a large microwavable safe dish. Microwave in 1 minute bursts, stirring after each time, until mixture is smooth and creamy. (It takes me about 4 minutes to get the mixture smooth in a small 700 watt microwave).
Stir in the vanilla and 1 cup of nuts (if desired). Pour the mixture into the prepared pan and spread into an even thickness. Top with the remaining nuts.
Pop the fudge into the fridge to let set. Cut into small squares and enjoy! (Keep refrigerated for best texture)