Start by cooking your potatoes until they are tender but not mushy. This can be done by boiling them in a pot of salted water for about 10 minutes, or by microwaving them for 5-6 minutes.

While the potatoes are cooking, heat the butter or oil in a large skillet over medium-high heat. Once the butter is melted or the oil is hot, add the chopped onion and sauté for 2-3 minutes until it becomes translucent.

Add the cooked corned beef to the skillet and stir it together with the onion. Cook for another 5-7 minutes, stirring occasionally, until the corned beef begins to brown and crisp up.

Add the cooked potatoes to the skillet and mix them in with the corned beef and onion. Use a spatula to gently press the mixture down into the skillet, creating an even layer.

Allow the hash to cook for 5-7 minutes, without stirring it, to allow the bottom layer to brown and crisp up. Use a spatula to flip the hash over in sections, so that the browned layer is now on top.

Cook for another 5-7 minutes, stirring occasionally, until the entire mixture is browned and crispy to your liking.