Heat 1 tablespoon butter (or olive oil) in a large stockpot over medium heat. Add onion and celery and sauté until soft and translucent (about 5 minutes). Stir in the garlic, fresh thyme, and Italian seasoning and cook for an additional 1-2 minutes.
Add in the vegetable stock, wild rice, mushrooms, carrots, bay leaf, a pinch of salt and pepper. Stir to combine.
Continue cooking until the soup reaches a simmer. Then reduce heat to medium-low, cover and simmer for 45 minutes, or until the rice is tender, stirring occasionally.
Meanwhile in a separate bowl whisk the flour, milk and heavy cream until combined. Gradually add the cream mixture to the soup and continually whisk until well combined. Also add in the butternut squash and kale at this time. Continue cooking, stirring frequently, until the mixture nearly comes to a simmer and has thickened and the butternut squash is tender.
Taste and season with salt and pepper. Serve or store in airtight containers. You could also freeze this soup once it has cooled.