Preheat oven to 350 degrees; butter and flour a 9-by-5-inch loaf pan (8-cup capacity), and set aside. In a large bowl, whisk together flour, brown sugar, baking powder, baking soda, and salt; set aside. In a medium bowl, combine butter, egg, and milk. Add wet mixture to dry mixture, and whisk to combine; fold in cranberries.
Pour batter into prepared pan; sprinkle top with turbinado sugar, if desired. Bake until a toothpick inserted in center of loaf comes out clean, about 1 hour and 15 minutes. Transfer pan to a wire rack; let bread cool 30 minutes. Invert onto rack, then immediately turn right side up to cool completely.