Preheat oven to 400 degrees.In a large bowl, stir together flour, sugar, baking powder, baking soda, and salt.Cut the butter into 1/2 inch cubes and distribute them over the flour mixture.
With a pastry blender or two knives used scissor fashion, cut in the butter until the mixture resembles coarse crumbs.
In a small bowl, stir together the buttermilk, egg, and vanilla. Add the buttermilk mixture to the flour mixture and stir to combine. Stir in currants or raisins, if desired.
With lightly floured hands, pat the dough into an 8-inch diameter circle on an ungreased baking sheet. Bake for 18 to 20 minutes, or until top is lightly browned and a toothpick inserted into the center comes out clean.
Remove baking sheet to a wire rack and cool for 5 minutes. Using a spatula, transfer the scone to the wire rack to cool. Cut into 8 wedges. Serve warm or cool completely and store in an airtight container.