Put the currants into a small bowl.
Heat the orange juice in the microwave or over the stove until very hot. Pour over the currants. Let the currants sit for 30 minutes, then drain them through a strainer.
Preheat the oven to 400 degrees. LIne a baking sheet with parchment paper.
In a large bowl, wisk together the flour, orange zest, baking powder, baking soda, salt, and sugar.
Grate the frozen butter and add to the flour mixture. Toss and coat the butter with the flour.
In a medium bowl, whisk the buttermilk, egg, and currants. Mix until just incorporated. Do not overmix. The dough will be shaggy.
If the dough is too dry, add 1 TBS of buttermilk at a time until all the flour is hydrated.
Turn the dough out onto a floured surface. Press the dough into a rectangle 3/4 inch thick. Fold one half of the dough over the other half. Press out and fold two more times.
Press out the dough until it is 1 inch thick. Cut out scones with a biscuit cutter. I used a 2 1/4 inch cutter. Reform the remaining dough and cut out the rest of the scones.
Put the scones on the baking sheet. Refrigerate for at least 30 minutes.
Brush scones with buttermilk and sprinkle with sanding sugar. Bake for 18-22 minutes until tops are golden brown.
Serve immediately. Enjoy.