Preheat oven to 375 degrees F (190 degrees C). Line a baking sheet with parchment paper or silicone baking mat.
Whisk all-purpose flour, whole wheat flour, oats, baking soda, baking powder, and salt together in a bowl. Cut butter into flour mixture using a pastry blender until mixture resembles coarse meal.
Beat buttermilk, egg, honey, and orange zest together in a bowl. Pour buttermilk mixture, currants, and raisins into flour mixture; stir with a wooden spoon until a wet, sticky dough comes together.
Turn dough out onto a well-floured work surface; press dough together into a soft ball of dough and cut into 2 pieces. Form each half into a smooth, round loaf. Transfer to prepared baking sheet and let rest for 15 minutes. Cut a 1/2-inch deep “X” into the top of each loaf with a serrated knife.
Bake in the preheated oven until golden brown and fragrant, about 45 minutes. Transfer loaves to a wire rack to cool completely before slicing.