Bring a large pot of salted water to a boil. Add the cubed potatoes and cook for about 15-20 minutes until tender.

Drain the potatoes in a colander and set aside.

In the same pot, melt the butter over medium heat. Add the chopped onion and sauté until translucent, about 5 minutes.

Add the spinach and cook until wilted, about 3-4 minutes. Season with salt and pepper.

In a frying pan, heat a little butter over medium heat. Crack the eggs into the pan and fry until the whites are set but the yolks are still runny, about 3-4 minutes.

Add the cooked potatoes to the spinach mixture and stir gently to combine. Adjust seasoning if necessary.

Serve the spinach and potato mixture on plates topped with a fried egg.