In a large pot (or large pan with deep sides), add the onion, celery, carrots, kosher salt, and pepper. Cook on medium heat for 10 min, stirring periodically (add a bit of water to the pan if getting to dry, to prevent burning).
Add the plant-based sausage, breaking it up into small pieces as you add it and/or break it up with a spatula in the pan. Stir and cook for around 12 to 15 minutes, stirring periodically, until the sausage is browned. You want some browning and crispness so that the texture is maintained during cooking.
Add the vegetable broth, plant-based milk, and the dried herbs. Stir.
In a small bowl, add cornstarch and 3 or 4 tbsp of the broth from the pot. Stir until well incorporated, then add this mixture back into the pot.
Stir in the nutritional yeast and bring to a gentle simmer and cook for 3 min (covered).
Add the white beans, cook another 3 min (covered).
Add the baby spinach, cook another 3 minutes as the spinach wilts.
Stir in the lemon juice prior to serving.