Preheat oven to 375°. Line 2 rimmed baking sheets with parchment paper.
In a large bowl, whisk together flour, granulated sugar, baking powder, and salt. Using a pastry blender or 2 forks, cut butter into flour mixture until it resembles coarse crumbs. Stir in walnuts and currants. Using a fork, stir in buttermilk, just until a dough begins to form. Working gently, bring mixture together with hands until a dough forms.
Turn out dough onto a lightly floured surface, and knead gently until smooth by patting dough and folding it in half 4 to 5 times. Using a rolling pin, roll out dough to a 3⁄4-inch thickness. Using a 2 1⁄2-inch Star of David cutter dipped in flour, cut as many scones as possible from dough without twisting cutter, rerolling scraps once. Place scones 2 inches apart on prepared baking sheets. Freeze until firm, approximately 15 minutes.
Lightly brush tops of scones with beaten egg, and sprinkle with white sparkling sugar.
Bake, one sheet at a time, until scones are golden brown and a wooden pick inserted in centers comes out clean, 14 to 18 minutes. Let cool on baking sheets for 5 minutes. Serve warm or at room temperature.
Recipe by TeaTime Magazine at https://teatimemagazine.com/walnut-currant-scones/