French Onion Flatbread

Ingredients

• 8 large yellow onions, peeled (about 2 pounds)
• 2 ounces unsalted butter
• Kosher salt
• ¼ cup sherry
• ¼ cup sherry vinegar
• 1 quart beef broth (fresh or store bought)
• Thyme, small tied bundle
• Mix together in mixing bowl
• 2 teaspoons (1 package) instant dry yeast
• 2 ½ cups lukewarm water
• 1 ½ teaspoons extra virgin olive oil
• 1 pound all-purpose flour
• 1 pound bread flour
• 4 teaspoons salt
• 1 medium shallot, minced
• 2 tablespoons sherry vinegar
• 1 tablespoon fresh lemon juice
• 1 teaspoon Dijon mustard
• 9 tablespoons extra-virgin olive oil
• Freshly ground black pepper
• 2 quarts Gruyere cheese
• 1 small celery root, peeled
• 1 kohlrabi, peeled
• 1 red radish
• 4 pieces of chive
• 12 celery leaves, pale green from inside bunch