Juice and zest of 1/2 small lemon (about 2 tbsp. juice and 2 tsp. zest)
1 cup chilled heavy cream
2 large egg yolks
1 cup unbleached all-purpose flour, plus more for dusting
1/4 cup sugar
1 tablespoon baking powder
3/4 teaspoon baking soda
1 teaspoon salt
3/4 cup (1 1/2 sticks) unsalted butter, cultured preferred, cut into 1/2-inch chunks, chilled
3 tablespoons unsalted butter, melted
1/4 cup Demerara sugar or turbinado sugar, optional
Soak the currants: Place the currants in a small glass or other nonreactive bowl, add the lemon juice and zest, and stir well. Let stand for 35 to 40 minutes. The currants will rehydrate and plump a little.
Prepare for baking: Preheat the oven to 400°F. Spray a rimmed baking sheet with nonstick vegetable oil spray or nonstick baking spray and set aside. In a small mixing bowl, combine the cream and egg yolks and whisk to combine. Cover with plastic wrap and refrigerate until ready to use.
Sift the dry ingredients: Sift the flours, sugar, baking powder, baking soda, and salt into the bowl of a heavy-duty stand mixer fitted with a paddle attachment or the bowl of a food processor fitted with a metal blade.
Add the butter: Scatter the butter chunks over the flour. If you are using a stand mixer, mix at medium-low speed for 30 seconds. If you are using a food processor, process in 8 (1-second) pulses. Either way, the mixture should resemble powdery sand in some spots and coarse sand in others. Do not overmix.
Add the egg mixture: Add the egg mixture and mix at medium speed for 30 to 45 seconds, or process in 4 (1-second) pulses, just until the dough barely comes together. It should be lumpy, with raggedy edges — not smooth at all.
Add the currants: Heavily dust a work surface with all-purpose flour. Scoop the dough out onto it (being careful of the blade if you are using a food processor), scatter the currants and zest on top, and gently mix them in.
Cut the dough: Divide the dough in half. Sprinkle a pinch of flour on top of one of the halves and shape into 6- to 7-inch round with a thickness of about 1/2 inch. Repeat with the other portion of dough. Use a pizza wheel or a large knife to cut each circle into 6 even wedges. Be sure to cut all the way through to the bottom so the wedges are separated. Using a pie server or a spatula, lift the wedges, one at a time, and arrange on the prepared baking sheet, about 1/2-inch to 3/4-inch apart.
Brush with butter: Brush the tops of the scones with the melted butter. Sprinkle with sugar if using.
Bake the scones: Bake until golden-brown on the tops and bottoms, 15 to 18 minutes.