How to Make It
Position a rack in the center of the oven and preheat to 400°F. Flour an 8-inch round cake pan. Line a half-sheet pan with parchment paper.
Whisk 1 ½ cups of the heavy cream together with the egg in a small bowl. Sift the flour, granulated sugar, baking powder, and salt together into a large bowl. Add the butter and toss to coat with the flour mixture. Using a pastry cutter or two knives, cut in the butter until the mixture is crumbly, with some pea-size pieces of butter. Add the currants and stir to coat. Make a well in the center of the flour mixture and add the cream mixture. Stir just until the dough holds together. Do not overmix. The dough will be sticky.
Transfer the dough to the prepared pan. Using floured hands, pat the dough evenly into the pan. Invert the dough onto the floured work surface. Using a sharp knife, cut the dough into eight equal wedges. Transfer the wedges to the lined pan, placing them 2 inches apart. Lightly brush each scone with the remaining cream and sprinkle with the sanding sugar. Bake until the scones are golden brown, 20 to 25 minutes. Let cool in the pan for 5 minutes. Serve warm. (The scones can be stored in an airtight container at room temperature for up to two days.)