Preheat the oven to 375 degrees F. Butter a baking sheet.
In a large bowl, combine the flour, sugar, and baking powder. Mix in the butter with your hands until coarse crumbs form. Add the eggs and buttermilk. Stir the mixture with a fork until the dough pulls away from the sides of the bowl.
Turn the dough onto a countertop and knead until the dough just holds together. Roll out or pat the dough into a 1/2-inch-thick rectangle. Cut into 12 triangles. Arrange the triangles on the baking sheet.
In a small bowl, beat together the egg yolk and milk and brush onto each scone. Sprinkle with sugar and bake for 20 to 25 minutes, or until golden brown.