01 - Preheat the oven to 400°F. 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. Cut it into the flour mixture using a pastry blender or your fingertips until the mixture resembles coarse crumbs.
04 - In a separate bowl, whisk together the heavy cream, egg, lemon juice, and vanilla extract.
05 - Pour the wet ingredients into the dry ingredients. Stir until just combined; do not overmix.
06 - Turn the dough onto a lightly floured surface. Gently knead a few times to bring it together, then pat into a 1-inch thick circle (about 7 inches wide).
07 - Cut into 8 wedges and transfer to the prepared baking sheet, spacing them slightly apart.
08 - Brush the tops with a little extra cream.
09 - Bake for 16-18 minutes, or until golden brown. Transfer to a wire rack to cool.
10 - For the glaze, whisk powdered sugar with lemon juice until smooth. Drizzle over cooled scones before serving.