Step 1

Turn on the Saute function on your slow cooker. Heat vegan butter and olive oil. Add leeks, onion, carrot, and mushrooms. Cook and stir until leeks and onions are translucent and softened, carrots have softened, and minced mushrooms have liquefied, about 7 minutes. Add potatoes and vegetable broth; mix well. Mix 1 tablespoon of the oat milk with potato starch to create a slurry and stir it into the soup.

Step 2

Heat remaining oat milk in a microwave-safe bowl in the microwave until hot, about 30 seconds. Pour it into the soup and season with salt and pepper. Turn off Saute function.

Step 3

Cook in the slow cooker on Low for 6 hours or on High for 3 1/2 hours. Stir soup before serving.