Melt butter in a pan and sauté onion, carrots, and garlic 3–4 minutes.

Toss mushrooms and flour into the pan to coat and cook 2 minutes.

Transfer mixture to slow cooker, add broth and thyme, and stir.

Cook on low 4–6 hours or high 2–3 hours until vegetables are tender.

Stir in half-and-half, season with salt and pepper, and warm 10 minutes before serving.