Potato and Portobello Mushroom Gratin

INGREDIENTS

• 1 tablespoon chopped fresh thyme
• 1/4 cup chopped fresh parsley
• 1 1/2 cups hot water
• 1 teaspoon ground black pepper
• 1 tablespoon chopped fresh rosemary
• 1 1/2-ounce package dried porcini mushrooms*
• 1 1/2 pounds portobello mushrooms
• 4 pounds Yukon Gold potatoes or white-skinned potatoes, peeled, cut into 1/8-inch-thick slices
• 12 tablespoons olive oil
• 4 garlic cloves, minced
• 2 teaspoons salt