In a large bowl, whisk together flour, sugar, poppy seeds, baking powder, salt, and lemon zest. Mixing them first ensures even distribution. The lemon zest spreads its flavor throughout the dough.
Add cold butter pieces into the dry mixture. Use a pastry cutter to blend until the texture looks like coarse crumbs. Keeping the butter cold helps create flaky layers in the oven.
In a separate bowl, whisk together the egg and soured milk. Pour this mixture into the dry ingredients. Gently fold everything together until just combined, being careful not to overmix.
Lightly flour your work surface and pat the dough into a circle. Cut it into wedges like a pie. Place the pieces on a lined baking sheet, leaving space between them.
Bake in a preheated oven until the tops are lightly golden. The scones should rise nicely and feel firm when touched. Let them cool slightly before glazing.
Mix powdered sugar, lemon juice, and butter until smooth. Drizzle the glaze over warm scones. Allow it to set before serving for the best texture.