01 - Preheat oven to 400°F. Line a baking sheet with parchment paper for easy cleanup and to prevent sticking.
02 - In a large mixing bowl, whisk together all-purpose flour, granulated sugar, poppy seeds, lemon zest, baking powder, baking soda, and salt until thoroughly incorporated.
03 - Add cold, cubed unsalted butter to the flour mixture. Cut into the dry ingredients using a pastry cutter or your fingertips until the texture resembles coarse crumbs with some pea-sized butter pieces remaining.
04 - In a separate bowl, whisk together heavy cream, egg, fresh lemon juice, and vanilla extract until uniform in consistency.
05 - Pour the wet mixture into the dry ingredients. Fold gently with a spatula just until combined; the dough should remain shaggy and may appear slightly dry. Avoid overmixing to prevent tough scones.
06 - Turn the dough onto a lightly floured work surface. Gently pat into a 7-inch circle approximately 1 inch thick. Cut into 8 equal wedges and transfer to the prepared baking sheet, leaving space between each scone.
07 - Lightly brush the tops of each scone with extra heavy cream. Bake for 16-18 minutes until the surface is golden brown and a toothpick inserted into the center comes out clean. Transfer to a wire rack and let cool completely.
08 - While scones cool, whisk powdered sugar with fresh lemon juice until smooth and pourable. Adjust consistency with additional lemon juice if too thick or more sugar if too thin.
09 - Drizzle the lemon glaze generously over the completely cooled scones. Allow the glaze to set for approximately 15 minutes before serving. Best enjoyed the same day but will keep for 2 days in an airtight container.