In a small bowl, whisk together flour, baking powder, salt and sugar.
Add the butter and use a pastry blender to cut in the butter until pea-sized lumps form.
In a separate small bowl or large measuring cup, whisk together the egg, milk and sour cream, then pour into the bowl with the dry ingredients and butter. Stir until a crumbly dough forms.
Turn the dough out onto a well-floured work surface and scrunch everything together and press down. You want to knead the dough but it will a little wonky at first. Just fold an edge over and press, fold another over and press. Keep going until it gets easier to knead cleanly and do so until a fairly smooth dough forms. It shouldn’t take more than 10 passes.
Shape the dough into a flat 1/2 inch thick disc about 9 inches in diameter. Cut into 8 slices.
Arrange on a baking sheet lined with parchment or a baking mat.
Brush with extra milk and then sprinkle each scone with turbinado sugar.
Bake for 17-18 minutes, until slightly golden on top and beginning to brown around the bottom edges.
Remove from oven and transfer to a wire baking rack to cool.