01 - Preheat oven to 375°F. Line a 12-cup muffin tin with paper liners or lightly grease each cup.
02 - In a large bowl, whisk together the all-purpose flour, whole wheat flour, sugar, baking soda, baking powder, and salt until well combined.
03 - In a separate bowl, whisk together the buttermilk, melted butter, and egg until smooth.
04 - Pour the wet ingredients into the dry ingredients and stir gently with a spatula until just combined; do not overmix.
05 - Fold in the golden raisins and orange zest until evenly distributed throughout the batter.
06 - Divide the batter evenly among the prepared muffin cups. Sprinkle tops with demerara or turbinado sugar if desired.
07 - Bake for 16 to 18 minutes, or until a toothpick inserted into the center comes out clean and tops are lightly golden.
08 - Let muffins cool in the tin for 5 minutes, then transfer to a wire rack to cool completely.