Measure chocolate and have it ready along with the vanilla.
Put sugar and milk in heavy sauce pan over medium heat. Stir with a wooden spoon to combine.
Do something else in the kitchen. In a few minutes the milk/sugar mix will come to a boil. Keep it on medium heat and boil for 2 minutes stirring with the wooden spoon.
Remove from heat and use whisk to beat in chocolate chips until no lumps remain.
Add vanilla and salt, stir to combine.
Use a heatproof spatula to scrape fudge into the buttered pan. Let it set. It will be firm enough to cut within 30 minutes.