Herbes de Provence – an aromatic mixture of herbs from southern France, including basil, lavender and thyme – enhances this smooth, slightly sweet, caramelized onion soup. Buttery croutons add crunch.
- 3/4 cup unsalted butter
- 5 pound sweet onions (such as Maui, Vidalia, or Walla Walla) peeled and thinly sliced
- 3 sprigs fresh thyme
- salt and white pepper (as needed)
- 1 tablespoon granulated sugar
- 1 tablespoon extra-virgin olive oil
- 2 celery ribs (chopped)
- 4 clove garlic (peeled, minced and divided)
- 1 tablespoon herbes de Provence
- 1 cup fino sherry
- 2 quart chicken or vegetable stock
- 4 cup rustic bread cubes
- 1 cup heavy cream
Melt ½ cup butter in a large enameled cast-iron casserole. Add the sliced onions, thyme sprigs and a couple of big pinches each of salt and white pepper and cook over medium heat, stirring frequently, until the onions soften and release their liquid, about 15 minutes. Lower the heat a little, add sugar and cook, stirring occasionally, until the onions are creamy and caramelized to a medium golden brown, about 1 hour and 30 minutes longer. Discard the woody thyme springs.
While the onions cook, heat olive oil in a medium skillet. Add celery, half the minced garlic, herbes de Provence and cook over moderate heat, stirring, until fragrant, about 3 minutes. Raise the heat to high and add sherry. Cook until the sherry has reduced by half, about 3 minutes. Scrape the celery mixture into the caramelized onions, add the stock and simmer over low heat for 30 minutes.
Preheat the oven to 400°. Melt the remaining ¼ cup butter in a small pan, add remaining minced garlic and continue to cook until fragrant, about 1 minute more. Spread bread cubes on a rimmed baking sheet and toss several times with the melted butter until well coated. Bake the croutons for about 10 minutes, tossing halfway, or until golden brown and crisp.
Add the heavy cream to the soup and simmer over low heat for 10 minutes. Use an immersion blender to blend the soup until completely smooth; reheat gently. Season with salt and white pepper. Ladle the soup into bowls, garnish with the croutons and serve.