Preheat the oven to 425°F. Grease and flour a baking sheet, or line it with parchment.
In a medium bowl, mix the flour, sugar, baking powder and salt until well combined.
Add the cold butter. Rub the mixture together with your fingers to break up the butter until it resembles fine breadcrumbs.
Add the milk slowly, mixing as you pour, using enough to bring the dough together with no dry lumps remaining. The dough should be quite sticky; if the listed milk is not enough, keep adding a little at a time until it is.
Spoon the dough onto a well-floured surface. Dust the top generously and knead 2 to 3 times, only to coat it in flour and smooth the surface. Press the dough into a round roughly 1 inch thick.
Using a well-floured 2 inch cutter, cut the dough into circles, pressing straight down and lifting straight up without twisting. Gather and press the scraps once to cut the last scones.
Place the rounds on the prepared sheet and brush the tops gently with the egg yolk and milk mixture.
Bake for 12 to 15 minutes, until golden and firm, adding up to 5 minutes if the tops are still pale.
Cool on a wire rack for 30 minutes before splitting. For softer scones, cover them with a clean tea towel as they cool.
Split each scone and dress with clotted cream and strawberry jam.