Heat the oven to 220°C/420°F. Melt half the butter over a medium heat and add half the garlic and plenty of salt and pepper, cook for a couple of minutes then add the mushrooms and fry for 10 minutes until softened then scoop out the mushrooms and set aside.
Add the rest of the butter, melt then add the rest of the garlic and flour. Cook for a couple of minutes then pour in the cream, whisking constantly until thickened. Season and remove from the heat.
Place the cooked pasta in a baking dish and pour over the sauce, add most of the parsley, all of the mushrooms and a handful of cheddar, mix until everything is combined. Top with the rest of the mozzarella and cheddar and bake for 15 minutes until browned. Sprinkle with the remaining parsley.
Nutrition information is an estimate and will vary depending on the exact ingredients used.