01 - Preheat oven to 400°F. Line a 12-cup muffin tin with paper liners or lightly grease with butter or cooking spray.
02 - In a large mixing bowl, whisk together all-purpose flour, whole wheat flour, granulated sugar, baking powder, baking soda, and fine sea salt until thoroughly blended.
03 - In a separate bowl, whisk together buttermilk, egg, and melted butter until the mixture is smooth and well combined.
04 - Pour the wet ingredients into the dry ingredients. Add dried currants and orange zest if using. Gently fold together with a spatula until just combined. Do not overmix—the batter should remain slightly lumpy.
05 - Divide the batter evenly among the prepared muffin cups, filling each about 3/4 full.
06 - Bake for 18–20 minutes, or until the tops are golden brown and a toothpick inserted into the center of a muffin comes out clean.
07 - Let the muffins cool in the tin for 5 minutes, then transfer to a wire rack to cool completely. Serve warm or at room temperature with Irish butter and jam.