In a large skillet, melt unsalted butter. Then, add chopped onion. Saute for 2-3 minutes or until tender.
Add chopped cooked potatoes and finely chopped corned beef, mix. Using a metal spatula, press down the corned beef hash. Cook on medium heat until brown (don't stir). Then, turn over the corned beef hash with a spatula and press down again. Cook until brown on the other side (don't stir the potatoes and corned beef).
Turn off the heat when the corned beef hash is brown on both sides. Add chopped parsley, freshly ground pepper and salt. Mix. Serve with fried/poached/scrambled eggs or salads.