In a large bowl, combine the flour, confectioners' sugar, baking powder, and salt.

Chop the cold butter into small chunks and add it to the dry ingredients. Work the butter into the flour mixture using your fingers until the mixture is crumbly.

Add the orange juice and mix until a dough forms. If needed, add 1-2 tablespoons of ice water, a little at a time, until the dough comes together.

Wrap the dough in plastic wrap and chill for 30 minutes.

Chop the raisins or currants into small pieces.

Preheat the oven to 350°F.

Roll the chilled dough into a thin rectangle, approximately ⅛-inch thick.

Lightly brush half of the dough with the beaten egg glaze, then spread half of the chopped raisins or currants over the glazed portion.

Fold the uncovered half of the dough over the fruit-covered half.

Press lightly over the dough with a rolling pin to even it out and help the layers stick together.

Brush the surface with the remaining beaten egg glaze.

Use a pizza cutter to trim the edges and cut the dough into approximately 2-inch squares or rectangles.

Sprinkle the biscuits with the granulated sugar.

Bake for 15-20 minutes, or until golden brown.

Allow the biscuits to cool completely before storing them in an airtight container at room temperature for up to one week.