Classic Crockpot French Onion Soup with Gruyere Toasts - My Home Made Recipe

Ingredients

• 5 large yellow onions, thinly sliced, about 3 lb (1.4 kg)
• 4 tablespoons (56 g) unsalted butter
• 1 tablespoon olive oil
• 1 teaspoon kosher salt, plus more to taste
• 1/2 teaspoon black pepper
• 1 teaspoon sugar, optional
• 3 cloves garlic, minced
• 2 tablespoons all-purpose flour
• 1/2 cup (120 ml) dry sherry or dry white wine
• 8 cups (1.9 L) low-sodium beef broth
• 1 tablespoon Worcestershire sauce
• 4 fresh thyme sprigs or 1 teaspoon dried thyme
• 1 bay leaf
• 12 slices baguette, cut 1/2 inch thick
• 1 tablespoon olive oil for brushing
• 2 cups (225 g) shredded Gruyere cheese
• 1/4 cup (25 g) grated parmesan cheese