Firstly, roast your garlic bulbs. Heat the oven to 180°C fan. Take the whole bulbs of garlic and slice about 1/2cm off the top of each. Spray with low-calorie cooking spray and wrap in a piece of tin foil. Place in the oven for 30-40 minutes.
Cook the potatoes in a pan of salted water for around 20 minutes, or until a knife slides easily into the centre.
While the potatoes cook, prepare the filling. Spray a large non-stick frying pan with low-calorie cooking spray, place over a medium to high heat and add the mushrooms. Cook for 6-7 minutes until browned. Remove from the pan and set to one side.
Spray the pan again with low-calorie cooking spray and add the leek and onions. Cook for 5 minutes until they begin to soften. Add the mince and cook for another 5 minutes.
Stir in the thyme and tomato purée. Add the Henderson’s relish and stock and bring to a boil. Return the mushrooms to the pan, then reduce the heat and simmer for 10 minutes.
While the mince cooks, unwrap your roasted garlic and squeeze the cloves out of their skin, into a bowl. Mash with a fork.
Drain the potatoes and mash with the cream cheese and half the roasted garlic. Season with salt and pepper to taste.
Stir the remaining garlic into the mince then add the cornflour slurry and stir until thickened. Season with salt and pepper, if needed.
Pour the mince into the ovenproof dish and top with the garlic mash.
Place on a baking tray and then place in the oven for 25-30 minutes until the potatoes are golden brown. Serve!