My brother makes this for brunch every weekend and we fight over the last piece.

Line an 8×8-inch baking pan or small baking sheet with aluminum foil, pressing it into the corners and leaving some overhang on the sides to create handles. Lightly mist the foil with nonstick spray or rub with a tiny bit of oil so the fudge releases easily.

Set up a heat-safe mixing bowl that will fit inside your slow cooker without touching the lid (you’re basically making a makeshift double boiler). Place the bowl in the slow cooker insert to be sure it fits, then remove it.
In the heat-safe bowl, add the sweetened condensed milk and chocolate chips. Pour in the cold brew coffee and stir briefly to coat the chocolate chips. The mixture will look loose and separated at this point—that’s okay.

Place the bowl back into the slow cooker insert. Pour hot tap water into the slow cooker around the outside of the bowl until it comes about halfway up the sides of the bowl, being careful not to splash any water into the fudge mixture.
Cover the slow cooker with the lid, set it to LOW, and cook for 45 to 60 minutes. Do not stir during this time; just let the gentle heat slowly melt the chocolate and warm the mixture through.
After 45 minutes, carefully remove the lid (watch for steam) and check the mixture. The chocolate chips should be glossy and mostly melted. Using a dry spatula or wooden spoon, stir the mixture slowly but firmly until completely smooth and thick. If a few unmelted chips remain, cover and let it go another 10 to 15 minutes, then stir again until fully melted.

Once the mixture is smooth and shiny, work somewhat quickly: pour about two-thirds of the fudge into the foil-lined pan, spreading it into an even layer with a spatula. The texture should be thick but spreadable.
Pour the remaining fudge over the top in a few uneven lines or dollops, then use the tip of a butter knife or a skewer to gently swirl the layers together. Drag the knife in small figure-eights to create visible ribbons of darker and lighter fudge, mimicking the look of swirled espresso and sweet cream.

Tap the pan gently on the counter a few times to release any air bubbles and to level the top. Let the fudge cool at room temperature for about 30 minutes, then transfer the pan to the refrigerator.
Chill the fudge for at least 3 hours, or until very firm. For the cleanest squares, let it chill overnight so it slices neatly and holds its shape on a brunch platter.
Once fully set, use the foil overhang to lift the fudge out of the pan and onto a cutting board. Peel back the foil. Using a sharp knife, cut into 24 small squares (or larger pieces if your family loves big bites). Wipe the knife with a warm, damp cloth between cuts for the neatest edges.

Serve the fudge cold or slightly chilled. Store leftovers in an airtight container in the refrigerator for up to 1 week, layering pieces with parchment or wax paper to prevent sticking.
Variations & Tips