Peel, wash and slice the potatoes. Peel and chop onion and garlic. Heat oil in a pan. Fry the potatoes for about 15 minutes. Turn from time to time.
Put the beans in a sieve, rinse and drain. Add onion, garlic and beans to the potatoes and fry for another 5 minutes. Season with salt and pepper. Mix eggs and milk. Season with salt and pepper and pour over the potatoes.
Let it falter at low heat. Wash parsley and chop finely. Serve the potato tortilla sprinkled with parsley. Serve with a green salad.