Add all the ingredients, (except the flour, milk, and extra salt and pepper) to the Instant pot and stir to combine. Select pressure cook, high pressure and set the timer for 45 minutes. Do a quick release of pressure and remove lid.
Turn on the sauté setting of the electric pressure cooker and stir in the flour and let cook for 2 minutes to get rid of the floury taste. Add the milk and stir. Bring to a boil to thicken, 2 minutes. Taste and adjust the seasonings as desired. Serve hot with some good, crusty bread.
If the soup seems too thick, add some additional vegetable broth to thin it out.