To your slow cooker add chopped onion, minced garlic, carrots and optional potatoes. If using potatoes, peel and slice into 1 inch cubes. Sprinkle with seasonings and shredded cheese. Pour in chicken broth and beer. Cover and begin cooking for 4 hours on high, or 8 on low.
Meanwhile, in a skillet over medium high heat melt butter. Add whole bratwurst, searing on each side. Remove, slicing into 1/2 inch pieces. Return to skillet to sear on each side. Remove and slice each piece in half. Carefully add to slow cooker. Cover and continue cooking.
In your last 30 minutes of cooking, remove 1/2 cup liquid to a large bowl. To it add flour and heavy cream. Stir well. Return to slow cooker giving a good stir and replacing cover to finish cooking.