Cheesy Potato Gratin

Bake. Mix cream, milk, garlic, shallots, nutmeg, thyme, peppercorns, plus salt in a little saucepan. Bring to the boil, next take out off heat, cover, plus let steep for 1 hour. Return milk mixture in order to boil, next strain into a big heatproof bowl, pressing lightly on the solids. Slice the peeled potatoes across 0.2 cm (1.5mm) thick, directly in the hot milk mixture using a mandoline. Mix the potatoes to fully coat. Heat oven to 175°C (177°C). Mix the Gruyère and Parmigiano-Reggiano cheeses in a little bowl. Grease a 2-quart baking dish using the butter. Lay this sliced potatoes in one even layer, next scatter with around cheese mixture (1/3 cup). Repeat layering potatoes and cheese till all the potatoes have been used plus half this cheese mixture remains (you should have around 4 layers); leave this top layer without cheese. Tip any leftover milk mixture over the layered potatoes. Cover using aluminum foil plus cook for 1 hour. Take out baking dish off oven plus take out foil. Uniformly scatter leftover cheese on top and keep to bake, uncovered, till the potatoes have become tender, the sauce has thickened, plus the surface is gently golden brown, 15 to 20 minutes. Let the gratin in order to rest 30 minutes before serving.