Place the chicken breasts in a single layer in the base of the slow cooker.
1 pound boneless, skinless chicken breasts
Add the celery, carrot, onion, and garlic to the slow cooker.
1 rib celery, 1 large carrot, 1 yellow onion, 2 garlic cloves
Pour in the chicken broth and add the wild rice, thyme, and bay leaves.
4 cups chicken broth, 1 cup wild rice, ½ teaspoon dried thyme, 1 bay leaf
Cook on high for 4 hours or low for 6 hours.
Remove the chicken from the slow cooker and place on a cutting board. Shred or slice the chicken. Add the chicken back to the slow cooker.
Stir in the heavy cream, butter, and mushrooms (if using).
1 cup heavy cream, 2 tablespoons unsalted butter, 1 cup sliced mushrooms
Cook for an additional 45 minutes on high or 1.5 hours on low.
Serve.