Preheat oven to 350°F. Prepare a baking sheet by lining with parchment or a silicone baking mat.
In a bowl (or food processor) combine flour, sugar, baking powder, cardamom and salt. Mix well, or if using food processor, pulse a few times. Blend in cold butter with a pastry blender, fork, or if using blender, pulse a few times until the mixture looks like Parmesan cheese.
In a small bowl, whisk together buttermilk, egg whites, vanilla extract and juice. Pour into dry mixture and mix until just incorporated - do not overmix. The dough will be sticky and slightly wet.
Turn dough out onto a well-floured surface. Working quickly with floured hands, knead it a few times lightly, adding flour if the dough is too wet. Pat it into about a 9 inch circle.
Using a knife or bench scraper, cut the circle into twelve equal wedges. If you can separate them slightly so they have a little room between them when you place them onto the baking sheet.
Bake for about 18-20 minutes until they are lightly golden brown.
Meanwhile, whisk together confectioners' sugar and citrus juice to create a glaze.
Remove from oven and allow to cool for a few minutes. If desired, drizzle with glaze. Serve warm with butter or clotted cream.