Heat a large pot or dutch oven to medium heat, add butter and olive oil. Let the butter melt and then add the onion. Sauté for a few minutes until the onion is translucent.
Add carrots, celery, garlic and sauté for 5 minutes until the vegetables are slightly soft, stirring often.
Add the flour and stir until combined and most of the vegetables are coated. Stir for one minute. Add the thyme, Italian seasoning, onion powder, salt and pepper. Stir until to combine.
Add the chicken broth, milk and heavy cream and mix together. Cover the pot, reduce the heat to medium-low and simmer for 15-20 minutes.
Add the rotisserie chicken, spinach and gnocchi. Stir continuously for a minute and then let the soup simmer for another 3-4 minutes or until the gnocchi are cooked through. Remove the soup from heat and serve. Enjoy with warm crusty bread or biscuits!