French Onion Soup en Croûte | Under a Puff Pastry Crust

Peel the onions, cut them in half, and slice into thin half rings. Peel and finely chop the garlic. Rinse the thyme and shake dry. Coarsely grate the Gruyère.

Melt 40 g unsalted butter in a large, heavy casserole pot over medium heat. Add the onions and 1 tsp fine salt. Cook gently over low to medium heat, stirring occasionally, for about 30–35 minutes until deeply caramelized and golden brown.

Stir the chopped garlic and 25 g all-purpose wheat flour into the onions and cook for 1–2 minutes. Deglaze with 150 ml white wine, scraping up any browned bits from the bottom of the pot. Let it simmer gently for about 2 minutes.