Beef and Guinness casserole

Name: Beef and Guinness casserole
Prep time: 15 min
Cook time: 10 h
Total time: 10 h 15 min
Cuisine: European, British
Ingredients: 4 diced red onions; 1kg casserole steak (browned); 5 cloves garlic minced; 6 carrots chopped; 6 celery sticks chopped; 500g chestnut mushrooms; Dijon mustard 1tbsp; 2can of Guinness; 600ml water; 4bay leaves; 2 pots beef stock; 2tsp rosemary; 2 tsp thyme; 2 tbsp dark soy sauce; 1 tbsp worcestershire sauce; 5 tbsp tomato puree; Salt to taste; Pepper to taste; 1-2 tbsp of cornstarch in water