Combine the melted butter, sugar, eggs and vanilla. In a separate bowl, combine the flour, baking powder, salt and spices. Add the dry mixture to the wet mixture, and stir well till combined. The dough will be thick.
Add the walnuts and currants. Stir well to combine. Divide mixture into three and form into logs, about 10cm wide. Place on a lined baking tray. Brush with egg white.
Bake in the oven for 20 minutes, till golden brown. Remove from the oven and allow to cool for about 10 minutes.
Cut each log into 2cm slices. Lay the biscotti on the baking tray and place back in the oven for 10 minutes, or until golden brown. Cool thoroughly and store in an airtight container.