Heat the oven to 425 degrees F (220 degrees C).
Line a baking sheet with silpat or parchment paper.
In a mixing bowl, stir together the flour, baking powder, salt, baking soda, sugar and poppy seeds.
Using a pastry blender, a fork or your fingertips, work the butter into the dry ingredients until the mixture looks like coarse crumbs.
In a small bowl, whisk together the egg yolk, milk, lemon juice and lemon zest. Pour into flour mixture and stir until just combined.
Turn the dough out onto a lightly floured work surface. Knead very lightly and form a circle. (Add a little more flour to the dough if the dough becomes too sticky to handle).
Cut the dough into 4 wedges.
Place the wedges onto the prepared baking sheet. Bake for 12-15 minutes or until golden brown.
Let cool on baking sheet for a minute, then transfer onto wire rack.