In a large cast iron skillet, melt butter over medium heat. Once the butter foams, add oil. Add onion, and cook until translucent, about 3 minutes. Add potatoes, and stir to combine with onion. Cover and let cook 8 to 10 minutes until potatoes are tender, stirring about half-way through.
Add corned beef, and stir to combine. Season with salt and pepper. Spread mixture evenly across the bottom to the pan, and increase the heat to medium-high. As meat begins to sizzle, use a metal a turner to look at the bottom side of the mixture. Once the bottom has browned, use the turner to flip the mixture to brown the other side. Let cook until both sides are browned. Remove from heat. If desired top with fried eggs and crisp bacon. Makes 4 servings.