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, baking powder, baking soda, salt, and lemon zest until well combined.
03 - Add the cold, cubed butter to the dry mixture. Cut in the butter using a pastry cutter or your fingertips until the mixture resembles coarse crumbs with some pea-sized pieces remaining.
04 - In a separate bowl, whisk together the heavy cream, egg, lemon juice, and vanilla extract until smooth.
05 - Pour the wet ingredients into the dry mixture and stir until just combined. Do not overmix. The dough should be slightly sticky but manageable.
06 - Turn the dough out onto a lightly floured surface and gently knead it 3-4 times to bring it together. Pat into a 1-inch thick circle. Cut into 8 wedges and place them on the prepared baking sheet, spacing about 2 inches apart.
07 - Brush the tops with a little extra cream. Bake for 16-18 minutes, or until golden brown on top and a toothpick inserted into the center comes out clean.
08 - While scones cool on a wire rack, whisk together powdered sugar and lemon juice until smooth and drizzling consistency is reached.
09 - Drizzle the glaze over cooled scones. Allow glaze to set for 5 minutes before serving.