Step 1

Turn your slow cooker on to high. Brown the mince, then set aside.

Step 2

Fry the chopped onion, leek and carrot until softened slightly, then add the tomato puree, plain flour, basil and thyme and cook for a few minutes.

Step 3

Add the chopped tomatoes, beef stock, Worcestershire sauce and bay leaves, then stir. Check the consistency of the sauce now as it won't thicken once cooking. Reduce if necessary, re-add the beef mince and season well with salt and pepper.

Step 4

Transfer to the slow cooker and cook for four hours on high or seven on low.

Step 5

An hour before the filling is ready, boil the potatoes until tender.

Step 6

Drain and allow to steam-dry for a few minutes, then add the butter, milk, and half the cheese, and mash well.

Step 7

Fill a pie dish with the filling from the slow cooker, taking care to remove the bay leaves. It's not essential, but allow the filling to cool before topping to stop the potato sinking into the filling.

Step 8

Add the potato topping, then grill on high for five minutes until the potato starts to crisp. Add the remaining cheese and grill for a further five minutes.