1. Heat the butter in a large cast iron skillet on medium heat. Add the onion and cook for a few minutes, until translucent.

2. Add the corned beef and potatoes, and spread the mixture out evenly in the pan. Increase the heat to high or medium high and press down on the mixture with a metal spatula.

3. Do not stir the potatoes and corned beef mixture, but let them brown. If you hear them sizzling, this is good. Use a metal spatula to life up a corner to see if they are browning. Once nicely browned, use the spatula to flip sections over in the pan so that they brown on the other side. Press down again with the spatula. If there is too much sticking, you can add a little more butter to the pan. Continue to cook in this manner until the potatoes and the corned beef are nicely browned.

4. Remove from heat, stir in the chopped parsley. Add freshly ground black pepper and salt to taste.