Sweet potato cobbler

Name: Sweet potato cobbler
Cook time: 1 h 10 min
Total time: 1 h 10 min
Cuisine: American
Ingredients: 2 pounds sweet potatoes; 4 cups water; 1 cup granulated sugar; 1/2 cup brown sugar; 1 teaspoon ground cinnamon; 1/2 teaspoon ground allspice; 1/4 teaspoon ground nutmeg; 1/4 teaspoon kosher salt; 2 tablespoons unsalted butter; 1 teaspoon pure vanilla extract; 1 tablespoon orange zest; 2 cups all-purpose flour; 3 tablespoons granulated sugar, divided; 1 tablespoon baking powder; 3/4 teaspoon kosher salt; 4 tablespoons cold unsalted butter, cut into 1/2-inch cubes; 3/4 cup buttermilk; Whipped cream or vanilla ice cream, for serving