Slice potatoes into thin round pieces. Thinly slice mushroom as well. In a pan, add garlic oil, potatoes and let them heat up for a few minutes. Then add the milk. Season with salt, paprika and oregano.
While the potato is simmering, saute mushrooms in another pan until the water runs dry. Add to the potatoes and gently mix.
Pour into a baking dish and let it cook in a pre heated oven for 30 minutes at 220degrees C.
The milk will bubble about and what results is a creamy potato and mushroom gratin delight. As Nigella suggests, would taste great with oven roasted chicken.