Cook the Vegetables: In a large pan, melt the butter over medium-high heat. Add the mushrooms and onion, cooking until the mushrooms release their moisture and the liquid evaporates, about 10-15 minutes.
Add Garlic and Herbs: Stir in the chopped garlic and fresh thyme, followed by the flour. Cook, stirring frequently, until the flour turns a light golden brown, around 2-3 minutes.
Deglaze the Pan: Pour in the white wine (or broth) to deglaze the pan, scraping up any browned bits from the bottom.
Simmer the Soup: Add the vegetable or chicken broth and the cheese tortellini. Bring the mixture to a boil, then reduce the heat and let it simmer for about 10 minutes, or until the tortellini is tender.
Finish with Cheese and Spinach: Stir in the grated Parmesan cheese until melted. Add the chopped spinach and allow it to wilt.
Add Cream and Seasoning: Pour in the cream (or milk) and season with salt and pepper to taste. Stir to combine, then remove from heat