For the asparagus soup: bring 2 liters of salted water to the boil in a saucepan, peel the asparagus and cut off the ends, cut the asparagus stalks into 2-3 cm short pieces and cook in the boiling salted water for about 12 minutes.
Melt the butter in a saucepan, sweat the flour in it, add about 1 liter of asparagus water, stir until smooth. Remove the asparagus soup from the heat.
Mix the egg yolks with the cream and stir into the no longer boiling soup. Season the soup with elderflower syrup, lemon juice, salt and pepper, then add the asparagus pieces and heat briefly.
Cut the white bread into slices. Pluck the thyme leaves from the stalks and finely chop them. Brush the bread rolls with goat cheese and sprinkle with a little thyme. Place on a baking sheet lined with baking paper and preheated in a hot oven to 200 degrees, on the middle rack for about 5 minutes .gratinated.
Arrange asparagus soup with elderberry on plates, serve with a dollop of creamy sour cream and slices of goat cheese and white bread. Serve sprinkled with a little thyme.