Fall-apart slow-cooker beef brisket and ale casserole

Name: Fall-apart slow-cooker beef brisket and ale casserole
Prep time: 15 min
Total time: 15 min
Cuisine: British
Ingredients: 700/800 g beef brisket (visible fat removed, and remove any string); 2 onions (finely chopped); 3 sticks celery (finely chopped); 1 clove garlic (finely chopped); 1 tbsp cornflour; 3 carrots (chopped into small chunks); 500 ml ale (I just use a local ale, but you can use Guinness!); 1 can chopped tomatoes; 1 tbsp tomato puree; 1 beef stock cube or stock pot; salt and pepper; 1 tsp dried thyme; spray oil or low-calorie cooking spray