Open the cans of crushed tomatoes and tomato sauce and place them in the slow cooker.
Add the entire box of vegetable stock
Add the garlic, herbs, and pepper to the slow cooker pot.
Cook on low setting for 7 hours. The soup will slightly reduce and thicken up. If you're at home, stir occasionally. However, if you put this on while away, no worry although you might get a little "sticking" when you wash the crock.
If you want to add almond milk or other non-dairy milk, stir it in after 6 hours, whisk it in, and re-cover the crock for an additional hour. Note: if you are planning to can this soup, do not add the milk substitute.
Remove the rosemary and discard the stem.
This soup has a rustic texture with small flecks of tomato which is lovely. If you prefer to smooth it out, you may use an immersion blender. That's your preference.