01 - Preheat oven to 400°F. Line a baking sheet with parchment paper.
02 - In a large bowl, whisk together flour, sugar, poppy seeds, baking powder, baking soda, salt, and lemon zest until evenly distributed.
03 - Add cold, cubed butter to the dry mixture. Use a pastry cutter or fingertips to work the butter into the flour until the mixture resembles coarse crumbs with some pea-sized butter pieces remaining.
04 - In a separate bowl, whisk together heavy cream, egg, lemon juice, and vanilla extract until well combined.
05 - Pour the wet ingredients into the dry mixture. Stir gently with a spatula or wooden spoon just until the dough comes together. Do not overmix as this will result in tough scones.
06 - Turn the dough onto a lightly floured surface. Gently knead 3-4 times to bring it together, then pat into a 1-inch thick circle.
07 - Cut the circle into 8 equal wedges. Place wedges on the prepared baking sheet, spacing about 2 inches apart.
08 - Brush the tops of each scone with a thin layer of additional heavy cream for golden coloring.
09 - Bake for 16-18 minutes until tops are golden brown and a toothpick inserted into the center comes out clean. Transfer to a wire rack to cool completely before glazing.
10 - Whisk together powdered sugar and lemon juice until smooth and pourable. Add more juice if needed for desired consistency. Drizzle generously over cooled scones.