Steam, braise, or boil your corned beef. It will take 3 hours on the stove or in a 350-degree oven, 5 hours on high in a crockpot, or 1 hour on high in an Instant Pot. Let the corned beef rest for 30 minutes.
Dice the potatoes into ¼ inch cubes and cook in lightly salted boiling water until tender, about 10 minutes. Drain well.
Preheat a cast iron skillet over medium high heat. Add butter and potatoes.
Chop corned beef into ¼ inch cubes and add to skillet. Stir to combine with potatoes.
Add vinegar and spices, and stir well.
Reduce heat to medium and let corned beef and potato mix cook for 5 minutes without stirring, so a crust forms.
Serve with any style of eggs.