Grate the onion finely.

Mix the beef with the onion, black pepper, nutmeg, paprika, and salt very well.

Form the meat into walnut-sized balls and place them in the fridge for about 10 minutes to firm up a bit.

In a skillet over heat, add some oil and fry the meatballs until cooked through.

Peel the potatoes, wash them, cut them into cubes, and fry them in hot oil, being careful not to over-fry them so they don't harden when mixed with the meat.

Squeeze the lemons.

In a new skillet of appropriate size, add the meat, potatoes, lemon juice, and about 2 tablespoons of vegetable oil. Let them cook together for a bit to blend the flavors.