Heat the Dutch oven to a medium-hot temperature. Fry the ground beef and onions until the beef is dark brown and the onions are soft and starting to caramelize.
Add the garlic and stir through. Slowly add the beef stock, stirring to make sure anything stuck to the Dutch oven is removed. Add the carrots and peas, then cook until softened.
Combine in a cup the water and cornstarch until smooth. Mix into the boiling stew and stir until returned to the boil and thickened. Take off the heat.
Peel the potatoes then boil and mash. Stir in the butter and milk.Tip: The potato topping can also be made using leftover mashed potatoes or instant potato mix when camping.
Spoon the mashed potatoes gently over the stew, then sprinkle with the shredded cheddar cheese and Italian herbs.Tip: To make this a one-pot meal cook the mashed potatoes first then put them aside while making the beef component. Add back to the beef stew to finish.
Place the lid on and bake the cottage pie for 15 minutes at 300 degrees F (150 degrees C).