This recipe is adapted from my friend Alli, who's family calls it "chocolate lava." (I mean right? She uses chocolate chips and adds less sugar) It's basically the same recipe that my mother-in-law Kris uses, and she found it years ago in Mable Hoffman's "Chocolate Cookery."*You can sub 1 and 1/2 cups heavy cream in place of the evaporated milk.
Homemade Chocolate Sauce (Hot Fudge Sauce) - https://thefoodcharlatan.com/homemade-chocolate-sauce/