For the Spinach Soup with Garlic Croutons, collapse the spinach with the lid closed in a large frying pan over medium heat, drain in a colander.
Butter in the same frying pan will heat. Sauté onion and garlic, add spinach for about 5 minutes. Add soup, bring to a boil.
Reduce the heat, simmer gently with the lid on for about 10 minutes. Finely puree the soup, bring to the boil, season.
In the meantime, prepare the croutons. Heat butter in a frying pan. Sauté the garlic in it. Add the toast, toast for about 5 minutes until light brown, add the lemon zest and mix.
Whip the cream. Serve soup in deep plates, garnish with cream and croutons. Serve remaining croutons separately with spinach soup with garlic croutons.