Preheat the oven to 400F/200C. Chop up the tomatoes and peal garlic cloves. Cut out the center cores of the tomatoes (don't need to do that for cherry tomatoes). Place tomatoes and garlic onto a sheet pan. Roast for 30 minutes.
While the tomatoes are roasting, chop up the onion into small pieces. Preheat the pot, add some olive oil to the bottom of it, and add the onion. Caramelize the onions on low-medium heat until brown. Stir occasionally to avoid burning.
When the tomatoes are ready add them to the pot. Blend the ingredients. You can use countertop or an immersion blender. If you are using a regular blender make sure to cover the top with a towel to avoid splashes. Blend part by part and return to the pot.
Add the chicken or vegetable stock and spices. Cover the pot and let simmer for another 30 minutes.
Enjoy! Serve with croutons, roasted eggplant, grilled cheese, bacon, heavy cream, or whatever else comes to your mind!