Layered Potato Gratin

Ingredients

• 1 package refrigerated pie crusts a package with two crusts
• 1 tbsp rosemary chopped
• ¼ tsp ground pepper freshly milled if possible
• 2 cups Gruyère cheese shredded
• 1½ pounds Yukon gold potatoes
• 1½ pounds sweet potatoes
• 1 tsp kosher salt
• ½ cup heavy cream
• 1 garlic clove minced
• fresh rosemary sprigs for garnish