A rich mushroom stock melds together the caramelized onions and cheesy croutons that make Rach's french onion soup simply irresistible.
- About 1 cup fancy dried porcini mushrooms, a small bag, loosely packed
- 2 quarts beef bone broth or stock
- 1 cup white wine
- ¼ cup dry sherry
- 2 tablespoons demi-glace, or one 1-ounce container, optional but recommended
- 4 tablespoons butter
- 2 tablespoons extra-virgin olive oil (EVOO)
- 4 large or 6 medium onions, peeled, quartered and sliced
- Salt and black pepper
- 1 teaspoon ground white pepper
- 1 teaspoon ground dried thyme or a small bundle of fresh thyme
- 1 large bay leaf
- 1 teaspoon sugar
- 1 baguette, sliced on small bias about ¾ inch thick
- 4 tablespoons softened butter
- 2 large cloves garlic, halved
- About 4 cups shredded Gruyere cheese, 1 pound
- About 1 ½ cups grated Parmigiano-Reggiano cheese, ¼ pound
For the stock, in a saucepot, combine the mushrooms and stock and simmer to soften mushrooms, 8-10 minutes, at low bubble. Puree in a high power blender or with an immersion blender. To serve, add wine, sherry, and, if using, demi-glace, and cook at medium boil, 6-7 minutes, until alcohol aroma cooks away.
For the onions, melt butter into olive oil over medium heat in a Dutch oven or soup pot. Add onions and season with salt, black pepper, white pepper, thyme, bay and sugar, then soften 8-10 minutes, while stirring frequently. Reduce heat to very low and cook about 1 hour, stirring occasionally.
For the croutons, lightly spread bread on both sides with softened butter.
Heat a skillet over medium-high heat and preheat broiler. Line a baking sheet with foil.
Cook bread in skillet until well-toasted and golden on both sides. Rub the croutons with garlic.
To serve, remove bay and thyme bundle, if applicable, from stock.
Fill soup bowls with onions and top with stock and 2 toasts. Place on baking sheet, top toast with cheeses and broil to bubbly and brown.