Light and quick dinner with fresh spring vegetables!
Cook the spinach in boiling salted water and drain well. Cut the portobello mushrooms into 2 cm strips and briefly fry both sides in hot oil. Drain to remove the excess liquid.
Prepare the béchamel sauce: heat the butter and when it starts to froth sieve over the flour and mix well. Stir continuously while adding the milk. Stir until it thickens, leave to cool. Beat in the egg yolks and put aside. Add salt and pepper to taste with nutmeg or grated cheese.
Place the mushrooms in a medium-sized ovenproof dish, cover with the spinach, then pour over the béchamel. Grate cheese over the top and arrange the sliced tomatoes.
Bake at 180-200 °C until the top begins to brown (45-50 minutes).