For the sauce:
2 tablespoons butter
2 large onions, quartered and very thinly sliced
1/4 teaspoon dried thyme
1 bay leaf
Salt and finely ground black pepper
1/2 cup dry white wine
1/2 cup veal stock or beef consomme
3 tablespoons creme fraiche or sour cream
For the steaks:
2 1-inch-thick hanger steaks (1 pound each)
3 tablespoons extra virgin olive oil (EVOO)
About 2 teaspoons herbes de Provence
Kosher salt and black pepper
Olive oil potato chips, cornichons, watercress and grainy Dijon mustard, for serving
In a large skillet, melt the butter over medium heat. Add the onions, thyme and bay leaf; season with salt and pepper. Cook, partially covered, stirring occasionally, until the onions are extremely soft and a light-caramel color, 20-25 minutes. Add the wine and cook 1 minute. Add the stock and bring to a boil. Cook 1 minute, then remove from the heat and stir in the creme fraiche.
Meanwhile, heat a cast iron skillet over medium-high. Coat the steaks with 2 tablespoons EVOO, then sprinkle with the herbes de Provence; season. Using a paper towel, rub the skillet with the remaining 1 tablespoon EVOO. Add the steaks and cook, turning once, about 8 minutes for medium-rare. Let rest for 5 minutes.
Slice the steaks against the grain, divide among plates and top with the onion sauce. Serve with the chips, cornichons and watercress. Pass the mustard at the table.