I work in Switzerland, and the cafeteria at work serves a dull green, pureed soup of leftover vegetables every day. It's a pass-able, workhorse soup. But a few tricks can turn a dull soup into a delicious soup: enough starchy vegetables (e.g., potato, celeriac, squash) to make it thick, not watery, and browning the vegetables before adding the stock.
The variations are endless. The Swiss greenmarkets have chopped up mixed vegetables (it looks like mostly leeks, squash, spinach) for soup making at home.
This is also a vegan recipe that is easy to turn into a vegetarian (and even more delicious) recipe by adding dairy products at the end (cream, milk and/or parmesan cheese). Or you could go all out and cook some bacon initially, brown the vegetables in the bacon fat and garnish with crumbled bacon at the end. —minipanda
large or 2 small celeriac (aka celery root), large dice
leeks (white and pale green parts only), chopped into 1/4" pieces
cloves of garlic, large dice
vegetable / herb stock (see note in recipe)
Vegetable/Herb stock: I use vegetable bouillon cubes and herb bouillon cubes to make soup, because they are relatively cheap, and Switzerland is very expensive. I just chuck them into the pot with the 8 cups of water at the appropriate time. Perhaps you will make your own vegetable stock or herb stock (should fresh vegetables and herbs not be outrageously priced where you live). If you cannot find herb bouillon cubes, add 1 tsp dried herbs (e.g., 1/4 tsp dried parsley, 1/4 tsp dried dill, 1/4 tsp dried thyme, 1/4 tsp dried rosemary) to the water in lieu of the bouillon cube. Adjust salt to taste.
A note on chopping the vegetables: The soup is pureed in a blender at the end, so the vegetables do not be chopped nicely or that finely. Chopping the vegetables into small-ish pieces creates more of a surface area for browning and enables the soup to cook faster.
On leeks: After chopping the leeks, separate the rings/layers and float them in a large bowl of water. Any sand or dirt will sink to the bottom. Scoop the leeks out of the water and dry (I use a salad spinner).
In a large pot, add olive oil over medium high heat. Once the oil is shimmering, add chopped leeks.
Once the leeks start to brown, add the garlic. Keep a close eye to avoid burning the garlic. Add the celeriac (usually a minute after the garlic goes in). Brown the celeriac. Stir the vegetables to keep them from burning.
Once the vegetables are sufficiently browned, add your vegetable/herb stock.
Bring to a boil. Boil soup until the celeriac or other starchy vegetable is easily pierced with a paring knife. 20 minutes? depending upon the size of your dice.
Puree the soup in a blender in batches. Remember to only fill the blender part way to avoid the hot soup from exploding out of the blender. Also, I pour the blended soup in a large bowl and mix it all together before serving, to even out the odd contents of blended batches (all the celeriac in one batch vs. all the stock in another batch). Alternatively use a stick blender.
Add cream or milk and/or parmesan cheese, as appropriate.