Ingredients

• 1 1/2 pounds medium Yukon Gold potatoes
• 1 1/2 pounds medium red-skinned sweet potatoes (yams)
• 2 cups heavy whipping cream
• 1 1/4 cups (packed) coarsely grated Gruyére cheese (about 5 ounces)
• 1/4 cup (1/2 stick) butter
• 1 tablespoon minced fresh Italian parsley
• 1 tablespoon minced fresh rosemary
• 1 tablespoon minced fresh sage
• 1 tablespoon minced fresh thyme
• 2 garlic cloves, minced
• 1 1/2 teaspoons fine sea salt
• 3/4 teaspoon freshly ground black pepper