Melt the butter in a soup pot over medium heat, then add in the onion and celery. Sauté for 5 minutes.
Stir in the garlic and flour and cook, stirring often, for another 1-2 minutes to get the raw flour taste out.
Whisk in the vegetable broth until the flour has dissolved.
Add in the cream, potatoes, frozen mixed vegetables, and Italian seasoning. When the soup is almost boiling, reduce the heat and cover the pot with the lid slightly open. Let the soup simmer for 15-20 minutes or until the potatoes are tender. Stir the soup occasionally during this time to ensure nothing is sticking to the bottom of the pot.
If the soup becomes too thick, add a splash more vegetable broth. It's very important to season this soup generously or it'll taste bland, so taste and adjust as needed, then enjoy!
