Cut chicken breasts into bite-size pieces. Season with kosher salt and freshly cracked black pepper.
In a large soup pot over medium heat, add 1 tablespoon of butter and 1 tablespoon olive oil. When heated, add chicken and cook until golden, about 5-8 minutes. Remove the chicken from the pot and set aside.
Add the remaining butter and olive oil. When heated, add onion and mushrooms, and cook until the onion starts to soften, about 3-5 minutes.
Add garlic and Italian seasoning, and stir until fragrant, about a minute.
Add Marsala wine and stir, scraping the bottom of the pan to release all the browned bits (that’s flavour!) — about a minute.
Add back the cooked chicken, chicken stock, balsamic vinegar, and gnocchi. Cook at a gentle, bubbling simmer until the gnocchi is fully cooked, about 8-10 minutes.
Add cream and spinach, and stir until the cream is heated and spinach has wilted, about 5 minutes. Taste the soup, and add additional salt & pepper to taste, if necessary.
Serve garnished with fresh, chopped parsley and thyme leaves. Optionally, you can add a drizzle of balsamic glaze. Don’t forget the crusty bread for dipping!