Preheat the oven to 400°F. Lightly grease an 8" or 9" round cake pan., In a medium-sized mixing bowl, whisk together the flours, sugar, baking soda, salt, and currants or raisins., Using a mixer, a pastry fork or blender, or your fingers, work in the butter until it's evenly distributed and no large chunks remain., In a separate bowl (or in a measuring cup) whisk together the buttermilk and egg. Pour this mixture into the dry ingredients and mix to combine. The dough will be stiff; if it's too crumbly to squeeze together, add another tablespoon or two of buttermilk., Knead the dough a couple of times to make sure it's holding together, then shape it into a ball. Flatten the ball slightly, and place the loaf in your pan. Use a sharp knife to cut a 1/2"-deep cross in the loaf., Bake the bread for about 45 to 55 minutes, until it's golden brown and a cake tester or toothpick inserted in the center comes out clean. Remove the bread from the oven and brush the top with melted butter, if desired., Store for about 2 days, well wrapped, at room temperature; freeze for longer storage (up to about a month).