Cake flour is clutch in this recipe for creating a perfectly balanced fluffy, crumbly and moist scone texture. Soaking the poppy seeds in warm milk softens them a bit and helps release their nutty flavor when baked. To prevent the curd leaking out during baking, take care to really pinch and seal the two disks of dough together all around the edges.
Preheat the oven to 425˚ F. Heat the milk in a small saucepan or warm in the microwave until steaming. Remove from the heat and stir in the poppy seeds. Let stand until cooled, about 20 minutes. Stir in the lemon juice to thicken and sour the milk.
Whisk the cake flour, granulated sugar, baking powder, tea and salt in a medium bowl; work in the cold butter and lemon zest with your fingers until the mixture looks like coarse meal. Make a well in the center, then add the egg and milk–poppy seed mixture. Stir together until combined and a soft dough forms, gently kneading the dough in the bowl once stirring becomes difficult.
Divide the dough in half and gently pat each portion into a 6- to 7-inch disk (1/4 to 1/2 inch thick), lightly dusting the dough and your fingers with flour if the dough is too sticky. Transfer one disk of dough to a baking sheet and spread the lemon curd on top, leaving a 1-inch border around the edge. Place the remaining disk of dough on top of the curd and pinch the edges together to seal. Brush the top with milk and sprinkle with turbinado sugar. Score the dough into 8 wedges, cutting about halfway into the top layer of dough but not into the filling.
Bake until golden brown, 25 to 30 minutes. Transfer to a rack and let cool 5 to 10 minutes on the baking sheet. Slide off the baking sheet and onto the rack; let cool at least 45 more minutes. Cut into wedges along the scored lines.