01 - Set the oven to 400°F and line a baking sheet with parchment paper.
02 - In a large bowl, whisk together the flour, sugar, poppy seeds, lemon zest, baking powder, baking soda, and salt.
03 - Add the cold, cubed butter to the dry ingredients and cut it in using a pastry cutter or fingertips until the mixture resembles coarse crumbs.
04 - In a separate bowl, whisk the heavy cream, egg, lemon juice, and vanilla extract until combined.
05 - Pour the wet ingredients into the dry ingredients and stir gently until just combined, avoiding overmixing.
06 - Turn the dough onto a lightly floured surface and shape it into a 1-inch thick round disk. Cut into 8 wedges and transfer to the prepared baking sheet.
07 - Brush the tops of the wedges with a bit of extra heavy cream.
08 - Bake for 16 to 18 minutes or until the scones are golden brown, then cool on a wire rack.
09 - Whisk together powdered sugar and lemon juice until smooth, then drizzle over cooled scones before serving.