7 tablespoons cold unsalted butter, cut into 1/2-inch pieces
1/2 cup skim milk
1 large egg
Coarse sugar, for sprinkling
Preheat the oven to 425°. In a large bowl, mix the flour, sugar, lemongrass, baking powder, pepper and salt. Using 2 knives or a pastry blender, cut in the butter until it is the size of small peas. In a small bowl, whisk the milk with the egg. Make a well in the center of the dry ingredients and add all but 1 tablespoon of the milk mixture; stir until the dough is evenly moistened. Gather the dough into a ball and knead a few times, just until it comes together.
On a lightly floured work surface, pat the dough into a 7-inch round. Brush the dough with the remaining 1 tablespoon of the milk mixture and sprinkle with the coarse sugar. Cut the round into 8 wedges and transfer them to a baking sheet. Bake in the center of the oven for about 15 minutes, or until the scones are golden and springy to the touch. Cool the scones slightly and serve warm or at room temperature.
The scones can be stored in an airtight container for up to 2 days.