Clean the onions. Cut the white and light green diagonally into fine rings. Dab salmon dry and dice finely. Squeeze lime. Mix onions, salmon, lime juice, chilli flakes and 1 pinch of salt. Cover and leave to stand in the fridge for 20 minutes.
Peel the asparagus, cut off the ends and cut diagonally into 2 cm long pieces. Peel ginger and cut into slices. Cook the asparagus with ginger and sugar in 1 litre salted water for 8-10 minutes. Remove asparagus and ginger.
Heat 2 teaspoons of butter in a saucepan. Add curry powder and flour. Steam for 1 minute over a mild heat while stirring. Add asparagus water and coconut milk. Bring to the boil, cover and cook over a low heat for 7 minutes.
Season soup with salt.
Add the asparagus pieces to the hot soup. Serve asparagus-coconut soup with salmon ceviche.
Tip: If desired, serve additionally sprinkled with basil leaves.