01 - Preheat oven to 400°F and line a baking sheet with parchment paper.
02 - In a large bowl, whisk together flour, sugar, poppy seeds, lemon zest, baking powder, baking soda, and salt.
03 - Add cold, cubed butter to the dry ingredients and use a pastry cutter or fingertips to mix until the mixture forms coarse crumbs.
04 - In a separate bowl, whisk together heavy cream, egg, lemon juice, and vanilla extract.
05 - Pour wet ingredients into the dry mixture and stir gently just until combined; avoid overmixing.
06 - Turn dough onto a lightly floured surface and pat into a 1-inch thick round.
07 - Cut dough into 8 wedges and place them slightly apart on the prepared baking sheet.
08 - Brush the tops with a little heavy 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 create a thick but pourable glaze.
11 - Drizzle the glaze over cooled scones and allow it to set before serving.