Preheat oven to 350 degrees. Prepare baking sheet with parchment paper.
Combine dry ingredients- flour, sugar, baking powder, and salt, in a large bowl.
Whisk together egg yolk and milk and set aside.
Cut butter into flour, until butter is about the size of small peas. (I used a pastry blender, but you can also use a food processor for this step).
Gradually drizzle the milk and egg mixture into the dry ingredients. Stir to combine. Dough will be crumbly and dry. Add currants and zest.
Using your hands, knead dough until dough comes together. This will take a minute or two- do NOT add extra liquid unless absolutely necessary. Form into a disc.
Turn dough out onto lightly floured surface. Roll dough in a circle, until it is about 1 inch in thickness.
Slice into sixths. Place on cookie tray and bake for 25-30 minutes or until scones are set and lightly browned.