Clean, wash and cut broccoli into florets. Clean, wash and chop the carrots. Cook broccoli and carrots in boiling salted water for 4-5 minutes. Drain on a sieve.
Peel onions and cut them into fine rings. Heat the fat in a pan. Fry the onion rings briefly in it. Place the pizza dough with the baking paper in a quiche tin (approx. 29 cm Ø). Spread the vegetables on top and put the cream cheese in heaps with a teaspoon.
Wash the thyme, dab dry and scrape the leaves off the stalks. Mix crème fraîche, eggs, thyme, salt, pepper and a little nutmeg. Pour over the vegetables. Press the edge of the dough a little inwards.
Bake in the preheated oven (electric oven: 200 °C/ gas: level 3) for 40-45 minutes. If necessary, 10-15 minutes before the end of the baking time, mix 1 egg yolk with 1-2 teaspoons of water and a little salt and brush the folded-over edge of the dough with it.
Cut the cake into about 8 pieces and serve hot.