Preheat oven to 375°F (190°C). Line a rimmed baking sheet with parchment paper.

In a medium bowl, whisk cold milk, sugar, and salt until dissolved.

In a large bowl, whisk flour and baking powder together.

Cut 10 tablespoons cold butter into ½-inch cubes; blend into flour until pea-sized bits remain with some larger chunks.

Pour milk mixture into flour and stir with fork until large clumps form. Knead gently in bowl until dough comes together, then transfer to floured surface.

Roll dough into 14×8-inch rectangle. Microwave remaining 2 tablespoons butter until softened; spread evenly over dough.

Sprinkle currants evenly, pressing lightly. Fold bottom third up, top third down (like a letter), then fold in half crosswise. Roll gently to flatten to 8×4-inch rectangle.

Cut lengthwise in half, then crosswise into quarters for 8 squares. Place on baking sheet, spacing 2 inches apart.

Sprinkle tops with demerara sugar and flaky sea salt.

Bake 25–30 minutes until golden brown. Meanwhile, melt remaining 4 tablespoons butter, skim foam.

Brush scones with clarified butter once out of oven. Cool on wire rack. Serve warm or room temperature.