01 - Preheat the oven to 400°F. Line a baking sheet with parchment paper.
02 - Whisk together the flour, sugar, poppy seeds, lemon zest, baking powder, baking soda, and salt in a large bowl.
03 - Add the cold, cubed butter to the dry mixture. Using a pastry cutter or fingertips, incorporate until the mixture resembles coarse crumbs.
04 - Whisk the heavy cream, egg, lemon juice, and vanilla extract in a separate bowl until combined.
05 - Pour the wet ingredients into the dry mixture. Stir gently just until combined; avoid overmixing.
06 - Turn the dough onto a lightly floured surface and gently pat it into a 1-inch thick round.
07 - Cut the round into 8 wedges and place them evenly spaced on the prepared baking sheet.
08 - Brush the tops of the wedges lightly with cream.
09 - Bake for 18 to 20 minutes until golden brown and cooked through. Transfer to a wire rack to cool.
10 - Whisk powdered sugar with enough lemon juice to reach a thick but pourable consistency.
11 - Drizzle the glaze over cooled scones and allow to set before serving.