01 - Preheat oven to 400°F. Line a 12-cup muffin tin with paper liners or lightly grease with butter.
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 buttermilk, egg, and melted butter until smooth and fully incorporated.
04 - Pour wet mixture into dry ingredients. Add currants and orange zest if using. Gently fold together until just combined—do not overmix.
05 - Divide batter evenly among prepared muffin cups, filling each approximately 3/4 full.
06 - Bake for 18–20 minutes until tops are golden brown and a toothpick inserted into the center emerges clean.
07 - Let muffins rest in tin for 5 minutes, then transfer to wire rack to cool completely. Serve warm or at room temperature with Irish butter and jam.