Arrange a rack in your oven to the upper-middle position. Preheat the oven to 425ºF (220ºC). Line a sheet pan with parchment paper.

Add the flour, baking powder, lemon zest, and sugar to the bowl of a food processor. Pulse a few times to blend.

Add the butter. Pulse until it forms a chunky, sandy mixture, with pea-sized bits.

Combine the egg and milk in a medium bowl. Beat with a fork to blend. Spoon out 2 tablespoons of the mixture, and set aside.

Add the flour-butter mixture to the bowl, along with the poppy seeds. Stir quickly with a fork or wooden spoon until it forms a rough dough.

Turn out dough onto a lightly floured counter. Roll dough ¾-inch (2-cm) thick. Use a 2 ½-inch (6-cm) round cutter to press out circles of dough. It’s okay to gently gather up, and re-roll scraps once or twice.

Place the cut scones on the prepared pan. Brush the tops with the reserved egg-milk mixture. Bake 10 to 12 minutes, until the tops are lightly golden, and the bottoms deep golden.

Remove from the oven, cover with a dish cloth, and let rest like this to cool for 10 minutes before serving.