Soak currants in lukewarm water for 15 minutes..
Mix flours, salt and baking soda in a bowl. Add the softened butter and mix everything with hands until crumbly. Make a well in the center of the mixture.
Add beaten egg to the well. Add most of the buttermilk and work everything to a soft but not sticky dough, using more buttermilk, if needed. Finally, knead in the drained currants.
Preheat oven to 230°C (approximately 450°F). Knead dough on a floured surface until it is smooth and elastic. Shape into 2 balls and place on a parchment paper-lined baking sheet. Score each loaf 0.5 cm (approximately 1/4 inch) deep in the shape of a cross. Slide into a hot oven (middle shelf) and bake 20 minutes. Then reduce oven temperature to 200°C (approximately 400°F) and continue to bake for 20 to 25 minutes.