Preheat your oven to 400°F (200°C) and line a baking sheet with parchment paper.
In a large bowl, whisk together the flour, sugar, baking powder, and salt.
Add the cold, diced butter into the flour mixture. Use a pastry cutter or your fingertips to work the butter into the flour until it resembles coarse crumbs.
In a small bowl, mix the buttermilk and beaten egg together.
Pour the wet ingredients into the dry ingredients and gently mix until a dough forms. Be careful not to overwork the dough.
Turn the dough out onto a floured surface and gently knead it a couple of times. Pat the dough into a 1-inch thick round.
Cut out scones using a cookie cutter and place them on the prepared baking sheet. Brush the tops with extra buttermilk.
Bake in the preheated oven for 12-15 minutes, or until the scones are golden brown.
Remove from oven and allow to cool slightly before serving warm with jam and clotted cream if desired.