Preheat oven to 180 °C.
Mix yoghurt, milk, flour, herbs, salt and pepper.
Spread a little of this sauce on the base of an oven dish.
Layer half the potatoes on the sauce. Place onions, garlic and mushrooms in an even layer on top.
Cover with remaining potatoes and pour over the rest of the sauce.
Sprinkle with cheese, cover with foil and bake for 45 minutes. Remove the foil and bake for another 15 minutes or until golden brown and cooked.
Dried or fresh thyme is delicious in this dish.
You can replace half the potatoes with sliced butternut or sweet potatoes.