The chef's secret for a good hash is to use the flesh of freshly baked potatoes.
Heat enough oil to cover the bottom of a large skillet, add the chopped onion, and cook over low heat, stirring, until straw-colored. Mix the corned beef with the potatoes and carrot, scrape the cooked onion into the mixture, stir in the herbs, a light sprinkling of salt and pepper, and the corned beef cooking broth. Turn the hash mixture into the skillet, but don't mash it down. Cook over the lowest possible heat about 40 minutes.
With a spatula, loosen the hash around the edges. Make a deep crease across the hash at right angles to the handle. Tip the skillet and fold this half of the hash over its lower half. Loosen the bottom with the spatula to be sure it comes free of the pan. Hold a hot platter over the pan, invert the skillet and platter together. Let the hash drop out like an omelet - it should be well browned and crusty on top.