So this is completely ganked from Jacques Pepin. There was a repeat of a 2011 episode of 'Essential Pepin' on PBS this afternoon and I just had to try it.
Oh. My. God.
Onion soup is pretty much mindless. So is this one. But the late addition of egg yolk with wine makes this a total winner. I just had a giant bowl, and I can't wait to have it reheated for lunch tomorrow.
Serves 6 to 8
15–20 thin slices (1/4-inch-thick) baguette
3 tablespoons unsalted butter
2 medium onions, thinly sliced (about 3 cups). I used the mandoline for this and it took 2 minutes tops.
6 cups homemade chicken stock or low-salt canned chicken broth (I used a 32 oz box of unsalted chicken stock from the store, plus 2 cups of water)
1/2 teaspoon salt, or to taste
1/2 teaspoon freshly ground black pepper
2 cups grated Gruyère or Emmenthaler cheese (I used a mixture of both).
2 large egg yolks
½ cup sweet port. If you don't have port on hand (as I didn't) you can substitute pretty much anything. I used 1/4 cup of leftover sake, plus some dry vermouth. You could also use sherry, or a sweet red. Go nuts.
Arrange the bread slices on a cookie sheet and bake for 8 to 10 minutes, until browned. Remove from the oven and set aside. (Leave the oven on.) Melt the butter in a large saucepan. Add the onions and sauté for 15 minutes, or until dark brown. Resist the urge to keep the burner on high: You want the onions caramelized, not burnt.
Add the stock, salt, and pepper. Bring to a boil and cook for 20 minutes. Pepin advises pushing the whole mess through a food mill. Don't bother. If you're really bothered by onion pieces, you can run an immersion blender through it if you want. I wouldn't.
Arrange one third of the toasted bread in the bottom of an ovenproof soup tureen or large casserole. Sprinkle with some of the cheese, then add the remaining bread and more cheese, saving enough of the cheese to sprinkle over the top of the soup. Fill the tureen with the hot soup, sprinkle the reserved cheese on top, and place on a cookie sheet. Bake at 400 for approximately 35 minutes, or until a golden crust forms on top.
At serving time, bring the soup to the table. Combine the yolks with the port in a small bowl and whip with a fork. With a ladle, make a hole in the top of the gratinée, pour in the wine mixture, and fold into the soup with the ladle. Stir everything together and serve.
Have some extra bread on hand. Trust me.