Put flour and 1 pinch of salt on the work surface. Press a depression in the middle. Add 1 egg and 4-5 tablespoons of cream. Spread cold fat in flakes on the edge of the flour. Quickly knead all ingredients with cool hands to a smooth dough and cover and chill for about 30 minutes.
In the meantime, wash the asparagus. Break off or cut off the woody lower end. Pre-cook the asparagus in plenty of boiling salted water for about 2 minutes. Drain on a sieve and let it cool down a bit.
Roll out the short pastry on a floured work surface in a circle of approx. 28 cm Ø and line the greased tart mould (24 cm Ø) with it. Press the edge of the dough lightly. Pre-bake in the preheated oven (electric: 200 °C/ gas: level 3) for 10-12 minutes.
Peel and slice the onion. Heat the oil in a pan and fry the onion briefly while turning. Mix the remaining eggs, mustard and cream. Season to taste with salt, pepper and nutmeg.
Clean and wash the cherry tomatoes, dab them dry and spread them on the pre-baked pastry with the drained asparagus and onion wedges. Pour egg milk over them. Bake at the same baking temperature for about 60 minutes.
If necessary, cover with parchment paper after 3/4 of the baking time. Garnish with parsley as desired.