Cheesy Potato and Kale Gratin – Fustini's Oils & Vinegars

Ingredients

• 4 slices seeded rye bread
• 1 large bunch kale, ribs removed, leaves torn into 3" pieces, clean & dry
• 2 cups Gruyère, grated
• 1/2 cup Parmesan, grated
• 1 pound Yukon Gold potatoes, unpeeled, cut crosswise into 1/8"-thick slices, divided
• 1 pound sweet potatoes, unpeeled, cut crosswise into 1/8"-thick slices, divided
• 1 teaspoon dried thyme, divided
• Kosher salt, freshly ground pepper
• 2 1/2 cups heavy cream
• 2 garlic cloves, finely grated or pressed
• 3 tablespoons Fustini's Herbs de Provence olive oil, divided