I had half a small fennel bulb left and some last legs carrots and celery, so I chopped them up sautéed them in a pan with a bit of onion olive oil. After about 7 mins or so, I added a can of tomatoes and a can of water and let it simmer for a while. When it seemed done, I put it all in a jar with a bit of oat milk (but any dairy will do) and blended until smooth. I added a squeeze of lemon for a bit of added brightness, but it is fine without.