Add all ingredients to a slow cooker and toss to combine.
Set the cooker to LOW, cover, and let cook 2 hours, or until hot and bubbly.
Stir well and set cooker to WARM before serving right out of the cooker. If the dip is too thick, or thickens over time, simply add a few tablespoons of milk to thin it out.
Serve alongside rye Melba toasts or hearty whole-grain crackers, for dipping.
Leftover corned beef is the best way to prepare this recipe, though you may also find precooked corned beef in the grocery store near the refrigerated tubs of prepared side dishes. You can also get corned beef from the deli counter and ask for it to be sliced extra thick.