To keep this true to its Depression-era roots, the base stays at four simple ingredients: potatoes, onions, butter, and flour (plus basic salt and pepper). From there, you can adjust to your own kitchen. For extra richness, you can drizzle 1/4 cup of milk or evaporated milk over the top before cooking, but note that this makes it less traditional and slightly saucier.
If you need to stretch the dish further, add one more potato and a small onion and increase the salt slightly. For a slightly smokier flavor that still feels old-fashioned, sprinkle a pinch of paprika over the top layer before cooking. To prep ahead on a busy workday, you can slice the onions and measure the flour mixture the night before and store them in the fridge; slice the potatoes the morning of cooking so they don’t discolor.
Food safety tips: Keep the slow cooker covered as much as possible during cooking so it maintains a safe temperature. Use a clean cutting board and knife when prepping, and don’t leave the finished dish at room temperature for more than 2 hours; refrigerate leftovers in a shallow container within that time. Reheat leftovers thoroughly until steaming hot in the center (165°F/74°C) before serving. If your slow cooker has a hot spot, rotate the crock halfway through cooking (if safe to do so) to encourage even browning on top.
