Heat a large skillet over medium-low heat. Add the butter and olive oil. When the butter foams, add the sliced onions and a pinch of salt. Stir to coat.

Turn the heat to low and cook the onions, stirring every 5–7 minutes, for about 30–40 minutes until they are soft and golden-brown. If they start to stick, add a tablespoon of water.

When the onions are caramelized, add the minced garlic and thyme. Cook for 1 minute until fragrant. Deglaze the pan with the white wine or stock, scraping up any fond, and let the liquid reduce for 2–3 minutes.

While the onions caramelize, bring a large pot of salted water to a boil. Boil the gnocchi according to package directions, about 2–3 minutes, until they float. Scoop the gnocchi with a slotted spoon directly into the skillet with the onions.

If you want a creamier sauce, stir in the heavy cream and simmer for 1–2 minutes to thicken slightly.

Sprinkle the grated Gruyère over the gnocchi and onions. Gently toss everything together off the heat until the cheese melts into a silky coating. Season to taste with salt, pepper, and red pepper flakes if using.

Transfer to a serving dish or bake briefly under a hot broiler for 1–2 minutes for a lightly browned top. Garnish with chopped parsley and serve immediately.