Heat a skillet to medium and add butter
When the butter has melted, add chopped onion and saute until translucent.
While the onions are sauteing, mix corned beef, potatoes, and spices together in a bowl.
When the onions are translucent, add contents of the bowl to the skillet and increase to medium-high heat.
Stir to combine fully and cook for about 5 minutes until the hash starts to brown.
Using a spatula, pat mixture down firmly and cook for 7-10 minutes until it starts to form a crispy crust.
Flip the hash by either cutting into sections and turning each or place a plate upon the hash and holding the plate firmly, flip the pan onto the plate then slide the whole hash back into the pan.
Cook the other side for 7-10 minutes until hash has a crispy crust.
Remove from the heat to a serving platter.
Serve hot, season with salt and pepper to taste.