3 lb Yukon gold potatoes, sliced very thin (use a mandoline)
2 cups heavy cream
1 1/2 lb Gruyere, grated
Salt and black pepper, to taste
Pinch of fresh grated nutmeg
Chives, chopped, to finish
Directions
Caramelize the onions: melt the butter with the olive oil in a large pot over medium heat. Add the sliced onions and 1 tsp salt and cook low and slow, stirring often, for 45 to 60 minutes until deeply golden. Deglaze with a splash of water whenever they stick, and stir in the thyme and balsamic near the end. Cook until all the moisture has driven off, so they don't waterlog the potatoes. Do not under-brown them.
Preheat the oven to 375F. Warm the heavy cream in a small pot and season it well with salt, pepper and a pinch of nutmeg.
Slice the potatoes very thinly on a mandoline.
Build the gratin in a baking dish in three layers: a layer of overlapping potato slices, a good pinch of salt, a third of the caramelized onions, a handful of Gruyere, then a pour of the warm cream. Repeat twice more. Potatoes and cream are notorious for needing more salt than you'd think, so season each layer.
Make the top layer neat and even, pour over any remaining cream, and finish with a generous layer of Gruyere.
Cover with foil and bake 45 minutes, then uncover and bake another 30 to 45 minutes until the potatoes are tender, the top is deeply golden and the edges are bubbling and caramelized.
Rest 15 minutes so it sets, then scatter with chopped chives and serve.
Credit: Ryan Nordheimer (@ryannordheimer), his first viral fall recipe. Source reel: https://www.instagram.com/reel/Dern9cbxw_G/ . The exact quantities are behind a paid Substack paywall, so the ingredient amounts here are reconstructed from the video and his posted tips (an entire pot of caramelized onions, about 1 1/2 lb Gruyere, layered three times); the method follows the reel. His two tips: don't under-brown the onions (make them ahead if needed so all the moisture cooks off, or they'll waterlog the potatoes), and don't skimp on salt.
