Center a rack in the oven and preheat the oven to 400°F. Line a baking sheet with parchment or a silicone mat.
In a small bowl, stir the egg and cream together.
Whisk the flour, sugar, baking powder and salt together in a large bowl. Drop in the butter and, using your fingers, toss to coat the pieces of butter with flour. Quickly, working with your fingertips or a pastry blender, cut and rub the butter into the dry ingredients until the mixture is pebbly.
Pour the egg, cream and currants over the dry ingredients and stir with a fork just until the dough, which will be wet and sticky, come together. (Don't overdo it.) Still in the bowl, gently knead the dough by hand, or turn it with a rubber spatula 8 to 10 times.
Lightly dust a work surface with flour and turn out the dough. Divide it in half. Working with one piece at a time, pat the dough into a rough circle that's about 5 inches in diameter, cut it into 6 wedges and place it on the baking sheet. (At this point, the scones can be frozen on the baking sheet, then wrapped airtight. Don't defrost before baking, just add about 2 minutes to the baking time.)
Bake the scones for 20 to 22 minutes, or until their tops are golden and firm. Transfer them to a rack and cool for 10 minutes before serving, or wait for them to cool to room temperature.
Notes
It's best to use currants that are fresh out of the box. They're a little more moist and plump than those that may be have lying around for a while.
If the currants you've purchased are rather dried out and hard, put them in a bowl with hot tap water for a few minutes and then drain thoroughly before adding to the scone dough.