Summer Squash and Onion Gratin - Litchfield Farmers' Market

Ingredients

• 3 tablespoons softened butter
• Panko bread crumbs
• Kosher salt
• 2 medium yellow squash, sliced in ½ inch rounds
• 1 medium green zucchini, sliced in ½ inch rounds (for color or use 3 yellow squash)
• 2 small or 1 large red onion, sliced paper thin
• ¾ to 1 cup grated Gruyere Cheese
• ¼ cup plain, non-fat yogurt
• ¼ cup milk
• 2 to 3 tablespoons fresh thyme leaves
• 1 teaspoon sea salt
• Freshly ground pepper