Heat a large pot over medium high heat. Add the olive oil.
Add the onions and celery and saute until the onions are soft.
Add the zucchini, thyme, dill, salt and pepper and stir well.
Add the vegetable stock and cover the pot, letting the soup come to a boil.
Once it comes to a boil, reduce the heat to medium low and let simmer for about 20 minutes.
After 20 minutes, remove the pot from the heat and add the cream.
Puree with an immersion blender (or in a standard blender in batches).
Serve in bowls with some fresh dill (if desired).