Step 1Heat the oven to 350 degrees. In a large bowl, sift together the flour, sugar, baking soda, baking powder and salt.
Step 2Cut in the butter until the mixture is crumbly.
Step 3In a medium bowl, whisk together 2 of the eggs, the vanilla and buttermilk. Pour the buttermilk mixture over the dry ingredients, and stir together to evenly distribute. (The dough will be crumbly.) Stir in the currants.
Step 4Pour the mixture onto a lightly floured cutting board, and gently knead to form a cohesive mass. Be careful not to overmix, or the dough will be tough.
Step 5Scoop the scones using a large (4-ounce) scoop onto a parchment-lined baking sheet, or divide the dough into 14 portions (each portion will be about one-half cup), leaving 3 inches between each.
Step 6In a small bowl, whisk together the remaining egg with the milk to form an egg wash. Brush the egg wash over each of the scones.
Step 7Bake the scones until puffed, lightly browned and a toothpick inserted comes out clean, about 30 minutes, rotating halfway through baking for even coloring. Remove to a rack and cool slightly before serving.