Fresh Vegetable Tian

Ingredients

• 4 tablespoons olive oil, divided
• 2 medium baking potatoes, peeled and thinly sliced
• 1 small Japanese eggplant, thinly sliced on diagonal
• 1 small zucchini, thinly sliced on diagonal
• 4 plum tomatoes, thinly sliced
• coarse salt
• fresh ground black pepper
• 4 sprigs fresh rosemary
• 1 head garlic
• 1/3 cup shredded gruyere cheese
• crusty bread, sliced 1/2 inch thick and toasted,for serving (optional)