3tablespoonsunsalted butter, cut into 1/2-inch pieces, at room temperature
Lightly grease an 8 x 8-inch baking pan. Line the pan with parchment paper, allowing the excess paper to overlap on two of the sides, set aside. Add the chocolate and espresso powder into a large, heatproof bowl; set aside. Fill a saucepan with a little water (you want it about 1/4 full) and bring it to a boil. Reduce the heat to barely a simmer. Place the bowl containing the chocolate and espresso powder on top of the pot. Cook, stirring frequently, until the chocolate has melted and the mixture is completely smooth, about 8 to 10 minutes. Add in the sweetened condensed milk and butter and cook for another 2 to 3 minutes, or until the butter is completely melted. Remove from heat. Whisk in the Kahlua, vanilla, salt, and cinnamon. The mixture will be VERY thick. Scrape the fudge into the prepared pan and smooth the top. Refrigerate for at least 2 hours, or until firm enough to slice.
Gently run a butter knife around the edge of the pan to loosen the fudge. Remove the fudge and transfer it to a cutting board. Peel off parchment paper, then slice the fudge into small pieces. Serve at once or store in the refrigerator for up to 1 month. You may also freeze the fudge, in an airtight freezer safe container for up to two months.
For best results, follow recipe exactly as written. See post for tips and tricks!