So first of all put the pan onto the hob with a medium heat add the oil and fry the onions and carrots until they are soft.
Add the garlic and the mince and stir from time to time until the mince has fully cooked and then add the mushrooms and cook for a further few minutes.
Add tomato paste, the beef stock, the red wine (if you are adding it), and the dried thyme and mix so it is fully incorporated and then leave for an hour on low heat to simmer and thicken. Stir every 15 minutes to stop anything sticking to the bottom.
After an hour the filling should be ready and what I mean by this is that it should be a thick consistency. Leave to cool down.
Preheat the oven to 200 degrees celsius fan (220 degrees celsius without fan).
Peel and chop up the potatoes and boil them in a pan with water until soft.
Drain the water from the potatoes and then add the butter, half to 3/4 of the cheese, salt, pepper and garlic powder. Use a masher or a hand blender to mash the potato until there are no more lumps.
Now that the filling has cooled down and the mash is ready as well, place the filling into a suitable dish (such as a Pyrex dish) and place the mash on top of the filling.
Sprinkle the remaining cheese on top of the cottage pie and place into the preheated oven for around 30 minutes (unit the top is golden).