Let the fudge cool at room temperature until it is no longer warm to the touch, about 1–2 hours. Then cover the trays lightly with foil and refrigerate for at least 3–4 hours, or overnight, until the fudge is very firm all the way through.
Once chilled and set, lift the fudge out of the trays using the overhanging foil. Place on a cutting board. Use a long, sharp knife to cut into small, even squares, wiping the knife with a warm, damp cloth between cuts to keep the edges neat and the surface glossy.
Arrange the squares back in the foil trays or on a serving plate. Store the fudge covered in the refrigerator for up to 2 weeks. For the best texture and flavor, let the pieces sit out for about 10 minutes before serving so the chocolate softens just slightly but still holds those nice, dense, clean cuts.
For a stronger Baileys flavor, you can increase the Baileys to 1 cup and reduce the sweetened condensed milk slightly (use about 1 3/4 cans total), but keep in mind the fudge will be a touch softer and richer. If you prefer a milder, more kid-friendly version, use only 1/2 cup Baileys and add an extra 1/2 cup chocolate chips to keep the texture firm. You can also play with the chocolate: swap half the semi-sweet chips for dark chocolate chips for a deeper cocoa taste, or use all milk chocolate chips for a sweeter, creamier fudge. Just keep the total amount of chocolate the same so it sets properly. To dress it up without adding ingredients into the base, you can press a few chocolate chips or a light sprinkle of flaky salt on top right after spreading the fudge in the pan—this doesn’t change the simple 3-ingredient base but gives a pretty finish. If your slow cooker runs hot, prop the lid open slightly with a wooden spoon during the last part of cooking and stir more often to prevent scorching. For the cleanest cuts, chill the fudge overnight, use a long, sharp knife, and run the blade under hot water, wiping it dry between slices. This recipe also travels well: keep the fudge right in those foil trays, cover tightly, and tuck into a cooler for potlucks, just like my aunt has done for years.
