For me, the secret to a good corned beef hash is the crust on the bottom and top and yummy moistness in the middle. The only way I've been able to achieve this is to work in stages.
I like a little larger potato maybe a tiny bit smaller than cottage fries but bigger and distinct cubes than chopped hashbrowns. I cut my potatoes to size and microwave them until done. (I keep them moist by using a wet paper towel over the potatoes and then covering that with plastic wrap.)
In a hot cast iron skillet add bacon grease or olive oil. Saute garlic, green bell pepper or hot fresh jalapeno (without seeds - it will be mild and sweetish chili flavored) and onion until tender and translucent. No color on the veg. In the last 5 minutes I will add my finely chopped corn beef and cook into the veg to heat the corned beef. Then remove from heat and deglaze pan if necessary. If deglazing, reduce liquid to a syrup state and add to the beef and veg mixture.
To the hot skillet, add more oil of your choice. Add the potatoes and salt, pepper and garlic powder if necessary and let them brown up well on all sides. Avoid over stirring. Once they are browned, add the meat mixture and press down to form a firm disc. If necessary (meaning if the potatoes used up all the oil in the pan), add extra oil to the pan by drizzling it around the edge of the pan. Cook over medium to medium-high, DO NOT DISTURB! Don't stir, don't monkey with it. You will smell when it's brown and crusty. If your pan is well seasoned you should theoretically at this point, be able to place a plate or tray over the pan and invert the contents of the hash onto it, then transfer it back to a reoiled hot pan and finish cooking on the second side. Repeat for side two.
In a separate pan fry 2 eggs in bacon grease till done to your specs. Serve a wedge of corned beef hash with the eggs on top and some great English Muffins or toast! Grits go great with this on the side! :D