For the yellow omelette, peel and finely dice the onion. Whisk 4 eggs and cream, season with salt and pepper. Heat 1 tablespoon of oil in a coated pan with lid (approx. 24 cm Ø). Fry the onion until transparent.
Stir in whisked eggs. Covered and let stand for 6-8 minutes at low heat. Slide the omelette from the pan onto a plate. Wipe the pan clean with kitchen paper.
For the green omelette, grate parmesan. Clean, wash and drain the spinach. Wash the herbs and shake dry, pluck the leaves and chop finely. Whisk 4 eggs. Season with salt, pepper and nutmeg.
Heat 1 tablespoon of oil in a frying pan. Add the spinach and herbs and let them collapse for 2-3 minutes. Stir in whisked eggs. Sprinkle with parmesan. Cover and let it simmer on low heat for 6-8 minutes.
Slide onto the yellow omelette. Wipe the pan clean again with kitchen paper.
For the red omelette, wash and quarter the tomatoes. Whisk 4 eggs and tomato paste. Season with salt and pepper.
Heat 1 tablespoon of oil in a frying pan. Sauté the tomatoes briefly. Stir in whisked eggs. Spread goat's cheese in flakes evenly on top. Cover and let it simmer on low heat for 6-8 minutes. Slide out of the pan onto the green omelette.
Wrap the three omelettes first in parchment paper, then in aluminium foil. Weigh down with a board and chill for at least 1 hour. Serve the omelette with pesto.