Pre-heat the oven to 200 ºC. Add the sprouts to a pan of boiling water, set on a medium heat and cook for 4 minutes. Drain well.
Spray a small frying pan with low calorie cooking spray, set on a low heat, add the leeks and garlic and cook for 4 minutes.
Add the cream cheese, milk, ricotta, Cheddar, Parmesan and mustard to a mixing bowl and season with salt and pepper. Mix together until smooth and combined.
Place the leeks, sprouts and cranberries in an ovenproof dish and pour over the cheese sauce.
Sprinkle over the remaining Cheddar cheese and pop into the preheated oven for 15 minutes until the top is golden and bubbly.