In a large bowl, add the corned beef and potatoes and mix lightly. Add the broth, the onions, garlic, and mustard. Mix lightly.
Add the seasonings and spices, and mix well. Cover and refrigerate ideally overnight.
Heat half the butter and half the oil in a pan or skillet over medium-high heat.
[Heat water - eggs for poaching in a separate pan or pot]
When the foaming of the butter subsides, add the hash mixture. Press down and form into a pancake the size of the pan. Fry for 3 minutes now on medium heat.
Tighten up the sides of the cake and cook for another 4 minutes. Look for the underside to be brown and crispy.
Flip the hash using a large spatula (or use a plate on top, invert, and slide off into pan). Add the rest of the butter and oil as you flip the mixture.
Rise the heat to medium-high and cook for 3 minutes. Firm up the edges. Reduce the heat to medium, cook for 4 minutes more.
Finish poaching eggs or fry eggs in a separate pan.
Plate the corned beef hash and top with a poached egg (or pan-fried egg) and chopped parsley.
