Cook two small yellow potatoes in the boiling water until done. Peel the potatoes and use a spoon to smash them.
Coarsely chop the lettuce and set it aside for the next step.
Heat 1 tablespoon unsalted butter on medium heat in a pot.
When hot, add the garlic and minced onion until slightly brown.
Add lettuce and stir until wilted.
Add your vegetable broth and simmer uncovered for 1 minute.
Transfer lettuce in batches to puree soup.
Transfer back to the pot. Add heavy cream and mashed potatoes and stir until all heated.
Let the soup cool down to room temperature, and then place it in the fridge to chill out.
When serving, add croutons as topping and season with black pepper. If you use unsalted broth,add some salt to taste.