Melt half of the butter in a large saucepan.

Add the chopped spring onions and celery to the saucepan.

Cook gently for about 5 minutes, or until softened.

Pack the spinach into the saucepan.

Add the vegetable stock.

Bring the mixture to a boil, then reduce heat to a simmer.

Cover the saucepan and simmer for 15-20 minutes.

Transfer the soup to a blender.

Blend until smooth.

Return the blended soup to the saucepan.

Add the mascarpone cheese to the soup.

Heat gently, stirring until the cheese is fully incorporated and the soup is smooth.

Season the soup with salt and pepper to taste.

Heat the remaining butter with the olive oil in a frying pan.

Add the bread cubes to the pan.

Fry until golden brown, stirring occasionally.

Add the caraway seeds to the croutons during the last minute of frying.

Ladle the soup into 4 warmed bowls.

Sprinkle with the prepared croutons.