Heat 2 Tbsp bacon fat (or olive oil) in a large oven proof skillet on medium high heat. Add the onions. Brown the onions, stirring frequently, about 2-3 minutes.
Transfer the onions to a bowl.
Add another Tbsp of bacon fat (or olive oil) and Tbsp butter to the pan and add the potatoes and cook the potatoes for about 5 + minutes or until brown, stirring frequently. Sprinkle on salt & pepper to taste as you cook.
Transfer the potatoes to a bowl and add the ham to the pan, stirring frequently until the ham is heated through, 1-2 minutes.
Mix onion, potato and ham together. Add the eggs, stirring to distribute the eggs among the vegetables and ham and top with the parsley. As soon as eggs begin to firm up, remove from heat and transfer skillet to oven and bake for about 15 - 20 minutes.