Clean the asparagus and peel only the lower ends. Cook with the sugar and a pinch of salt for about 12-15 minutes.
For the sauce, stir the milk with the liquid butter, the egg yolk and the cornstarch until smooth. Then bring to the boil while continuing to stir. Remove the pan from the fire and add the cream, mozzarella and half of the chives and stir until the mozzarella has melted. Season to taste with salt, a little pepper and nutmeg.
Arrange the asparagus on plates, pour the sauce decoratively over it and put it in the oven preheated to 200 degrees. Baked for about 5 minutes.
Then remove, sprinkle with the diced tomatoes and the remaining chives and serve.
Boiled potatoes or croquettes are ideal as a side dish.