Henri's French Onion Soup | America's Test Kitchen

Ingredients

• 3 pounds yellow onions
• 3 tablespoons unsalted butter
• 1/2 teaspoon table salt, plus more as needed
• 1 pinch sugar
• 8 cups water, plus more as needed
• 1 tablespoon all-purpose flour
• 1 sprig fresh thyme
• 1/4 cup dry white wine
• 1 baguette, crusty
• 8 ounces Gruyère cheese (or Swiss), grated