Preheat oven to 180°C.
Layer half the potato slices over the base of a greased, ovenproof dish.
Top with butternut slices and sun-dried tomatoes and sprinkle with cumin.
Arrange the remaining potato slices on top.
Mix the sachet contents with a little of the cold milk to make a smooth paste before adding the rest of the milk.
Pour over the potatoes and sprinkle with grated cheese.
Bake in a preheated oven for 30-40 min until cooked through.