French Onion Potato au Gratin

Ingredients

• 4 pounds Yukon gold potatoes, peeled
• 2 cups 35% whipping cream
• 1 1/2 cups (150 grams) Gruyère cheese, grated
• 1 1./2 cups (150 grams) Emmental cheese, grated
• 1/2 cups panko breadcrumbs
• 1/4 cup (50 grams) Parmigiano-Reggiano, grated
• 2 tablespoons unsalted butter
• 4 garlic cloves, finely minced
• 1/2 tablespoon kosher salt
• 1/2 tablespoon extra-virgin olive oil
• Fresh cracked black pepper
• 5 cups Spanish onions, thinly sliced
• 1 tablespoon unsalted butter
• 1 tablespoon extra-virgin olive oil
• 1/2 tablespoon thyme leaves, chopped
• 1 teaspoon kosher salt
• Fresh cracked black pepper, to taste