Boil 3 eggs hard for about 10 minutes. Peel, wash, quarter and slice the potatoes. Heat the oil in a pan (24 cm Ø). Brown the potatoes. Rinse and peel the eggs.
Wash the zucchini, quarter them lengthwise and cut into slices. Clean and quarter the mushrooms. Add the zucchini and mushrooms to the potatoes after about 10 minutes. Clean and wash spring onions, cut them into slices and fry them.
Wash the marjoram, dab dry, pluck from the stalk and add to the vegetables. Whisk 4 eggs and milk well and season with salt and pepper. Pour egg milk into the pan and cover with a lid. Cook at low heat for 15-20 minutes until the egg milk has set.
Peel the garlic and press it through the garlic press. Halve the eggs. Mix egg yolk, garlic and vinegar. Add oil drop by drop. Season to taste with salt and pepper. Turn out the fritatta from the pan and cut into 12 pieces.
Serve the fritatta warm with the aioli.