2 pounds yellow onions (about 2 large or 4 medium)

1 small bunch fresh thyme, divided

2 tablespoons olive oil, divided

2 (16- to 18-ounce) packages fresh, shelf-stable, or frozen potato gnocchi (do not thaw)

2 tablespoons unsalted butter

1 teaspoon kosher salt, plus more as needed

1/2 teaspoon freshly ground black pepper, plus more for serving

6 ounces Gruyère cheese, grated (about 1 1/2 cups)

1/4 cup dry white wine

1 teaspoon balsamic or sherry vinegar

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Thinly slice the onions and strip the thyme leaves until you have 2 tablespoons.
Heat 1 tablespoon olive oil in a 12-inch broiler-safe skillet over medium heat. Add 1 package gnocchi in a single layer. Cover and cook undisturbed until golden on the bottom, 3–5 minutes. Transfer to a baking sheet. Repeat with remaining oil and gnocchi.
Melt butter in the skillet. Add onions, half the thyme, salt, and pepper. Cook, stirring often, until deeply golden and soft, 28–30 minutes.
Add wine, scraping up any browned bits, and cook until evaporated, about 1 minute. Stir in vinegar and remove from heat.
Return gnocchi to skillet, stir to combine, and adjust seasoning. Top with cheese and broil 4–6 minutes until bubbly and browned.
Garnish with reserved thyme and more pepper. Serve warm.

Use a cast iron or heavy broiler-safe skillet for best results.
Leftovers can be stored in an airtight container in the refrigerator for up to 4 days.
No need to boil the gnocchi—pan-frying keeps them crispy outside and tender inside.