Cherry and Cranberry Cobbler

Name: Cherry and Cranberry Cobbler
Ingredients: 2 sticks (1 cup) melted butter, cooled slightly, plus additional for buttering the pan; 1 3/4 cups all-purpose flour; 1/2 cup fine polenta, such as Bob's Red Mill; 1/2 cup powdered sugar; 1/2 teaspoon ground cinnamon; 1/2 teaspoon baking powder; 1/2 teaspoon kosher salt; One 10-ounce bag frozen cherries, thawed and drained; One 10-ounce bag frozen cranberries, thawed; 2/3 cup light muscovado sugar or light brown sugar; 2 tablespoons all-purpose flour; 1 teaspoon orange zest (from 1/2 orange); 1/4 teaspoon kosher salt; Serving suggestion: whipped cream or vanilla ice cream