Pre-heat oven to 350°F degrees.
In a small bowl, add the egg and water; mix thoroughly to combine; set aside.
Line a sheet pan with parchment paper or baking mat.
In a large bowl, toss dry ingredients and zest together; using your fingertips or a pastry cutter, rub butter and flour mixture together just until butter pieces are the size of peas and covered with flour.
Make a well in the center of the bowl and pour in egg and cream; mix ingredients together by hand until a shaggy dough is formed.
Turn out onto a floured surface and gently mix in currants, kneading dough and currants together just until incorporated.
Pat dough into a ¾-inch to 1-inch-thick rectangle.
Cut rectangle in half lengthwise, then cut across into 8 or 12 smaller rectangles.
Place them on the baking sheet with sufficient space between each scone.
Brush tops with the egg wash and sprinkle with brown sugar.
Place in the pre-heated oven and bake until light golden brown; about 25 minutes; rotate the pan front to back halfway through.
Remove from the oven and let scones cool slightly on the baking sheet.
Serve warm or at room temperature.
Best if served within 24 hours.
