Butter the bottom and sides of an 8 by 8-inch baking pan. Line the pan with a sheet of parchment paper, allowing a couple inches of parchment paper to hang over the sides.

In a medium glass or stainless steel bowl, combine the condensed milk, cinnamon, and vanilla. Stir in the chocolate chips and butter. Put the bowl on top of a saucepan of barely simmering water and stir until the chocolate chips have melted and the mixture is smooth, about 6-8 minutes. (You can also add nuts at this point if you like them). Using a spatula, scrape the mixture into the buttered pan and smooth the top. Refrigerate for at least 2 hours until firm.

Holding the edges of the parchment paper that are hung over the pan, lift the fudge out of the pan and onto a cutting board. Peel off the parchment paper and cut the fudge into 1-inch pieces. Store refrigerated in an airtight container or freeze. That is . . . if you don’t eat all of it while standing in the kitchen.