Place mushrooms, garlic, basil, oregano, thyme and bay leaves into a 3-qt slow cooker. Stir in vegetable broth; season with salt and pepper, to taste.
- Cover and cook on low heat for 3-4 hours or high heat for 1-2 hours, or until browned and tender. Stir in half and half and butter during the last 15-20 minutes of cooking time.
- Serve immediately, garnished with parsley, if desired.