Preheat the oven to 425° F Place an oven rack in the upper third of the oven. Grease a baking sheet with shortening or vegetable cooking spray. Place the flour, baking powder, sugar, salt, and butter in a food processor fitted with the metal blade, or in the bowl of a mixer. Process, or mix at low speed, until the mixture is in coarse crumbs. Add the lemon peel, eggs, yogurt, and currants; mix until thoroughly combined. Remove the dough to a floured surface and pat it into a ball; it will be sticky. Roll it with a floured rolling pin into a 9-inch circle about 3/4 inch thick. Cut out rounds, squares, or hearts, using a 2" cookie cutter dipped in flour. On a baking sheet place the scones about 1 inch apart. Gather up scraps of dough and pat them into a 3/4" thick disk. Continue cutting and patting out dough until all scraps are used. Brush the tops with the egg glaze. Bake for 7 to 9 minutes or until golden. The scones may be covered and held at room temperature overnight, or frozen. Reheat them at 350° for 5 minutes or until hot. Cut the scones in half and serve warm with Lemon Curd.