Preheat the oven to 425˚F (or 400°F convect) and line a baking sheet with parchment paper or a Silpat liner.

In a large bowl, add the flour, baking powder, and salt. Cut the cubed butter into the flour mixture until it has a fine, sandy texture. Avoid large clumps of butter as that diminishes the rising.

In a small bowl, warm the buttermilk slightly and add vanilla. Set aside. (See notes for making your own buttermilk)

Whisk in the sugar into the flour mixture, make a well in the center and pour in the buttermilk. Gently mix until the dough is just combined.

Transfer the dough onto a floured surface, and fold the dough over 2 to 3 times—Pat into a round shape, about 4cm or 1 1/2 inches thick.

Cut out dough circles and place them onto the prepared baking pan using a floured 2-inch round biscuit cutter (or cookie cutter or the rim of a glass). Pressing the cutter straight down and straight up without twisting or pulling the dough is important. This impacts the scone's rise. Brush the tops with the egg wash.

Bake for 10 to 12 minutes or until risen and golden. Let cool slightly.

Serve warm with jam and clotted cream or lemon curd.