Preheat the oven to Gas Mark 5 (375F degrees).

Slice the potatoes as thinly as you can (1/4 inch thickness or less).

Combine the milk, cream, ricotta, garlic, nutritional yeast (if using) and salt in a large bowl and whisk together until smooth.

Add the sliced potatoes to the bowl and stir gently so that all the slices get coated in the cream mixture.

Remove the potato slices using a large spoon and place into a 9 inch square roasting dish. Pour any remaining cream mixture over the top and using the back of the spoon, gently press the potatoes down.

Cover the dish with foil and bake on the middle oven shelf for 45 minutes.

Remove the foil, press down the potato slices again to keep the top layer from drying out, then return to the oven until most of the cream is absorbed and the potatoes are tender (mine took another 30 minutes).

Scatter the shredded cheese over the top and bake for a further 10 - 15 mins or until the cheese is melted and bubbling.

Leave to stand for a few minutes before serving.