Preheat the oven to 375°F.

Use a  food processor fitted with a shredding blade to grate the frozen butter as you would cheddar cheese.

Mix together the oats,  flour, currants, sugar, baking  powder, baking soda, and salt.

Separately,  whisk the  egg into the heavy cream; take out about two tablespoons of this wet mix and set aside.

Pour the remainder into  a center well of the dry mix and toss from underneath to blend, trying not to touch it too much, until  the flour works almost  completely  in.

Turn out onto a parchment lined baking sheet and pat into a disk one inch thick,  touching up the sides.

Use a chef's knife to cut the dough into wedges.

Brush  the top with the reserved egg/cream, then sprinkle with sparkling sugar.