Place the diced potatoes in a large pot of salted water and bring to a boil over high heat. Cook for about 4-5 minutes until they are slightly tender but still firm, then drain well to remove excess moisture.

In a large cast-iron skillet, heat the butter and vegetable oil over medium-high heat until shimmering. Add the chopped onion and green bell pepper, sautéing for 3-4 minutes until the onions are translucent and softened.

Add the par-boiled potatoes and diced corned beef to the skillet, stirring once to mix the ingredients. Spread the mixture out into a single, even layer across the pan and press down firmly with a spatula.

Cook undisturbed for about 5-6 minutes, allowing a deep golden crust to form on the bottom. Flip the mixture in sections, press down again, and cook for another 5 minutes until crispy and browned throughout.

Season with salt and black pepper to taste, keeping in mind the corned beef is naturally salty. Remove from heat, garnish with fresh chopped parsley, and serve immediately, ideally topped with a fried or poached egg.