Put the flour in a large bowl, and grate the lemon zest over the top. Keep the lemon for the glaze later.
Add the cold butter and rub it through the flour. Then add the cold buttermilk.
Use a sharp knife dipped in flour to cut the dough into squares, then cut each square in half to make triangles.
Place the cut scones, close together, on the lined baking sheet. Bake for 15 minutes in a regular oven or 12 in a steam oven.
Make a sweet lemon glaze by combining powdered sugar with lemon juice. Drizzle the glaze onto the scones and serve.