Arrange oven rack to middle of oven, then preheat to 400°F. Line baking sheet with parchment paper.

In large bowl, sift together flour, baking powder and baking soda; whisk in sugar and salt. Using coarse side of box grater, grate in butter; toss to combine. Using fingertips, break up shortening into small pieces and work into butter mixture until it resembles coarse cornmeal. Stir in currants and lemon zest.

Using a fork, gently stir in cream until mixture is incorporated and forms a shaggy ball. Turn out onto a lightly floured surface and gently roll out into 1-inch thick round.

Using a 2-inch round cutter dipped in flour, cut out rounds, pressing scraps and patting into 1-inch thickness.

Arrange scones 2 inches apart on prepared baking sheet. Lightly brush tops with some 35% cream and sprinkle with a little sugar.

Bake on middle rack of oven until scones are lightly golden, 15 to 18 minutes. Serve immediately.