01 - Preheat oven to 400°F. Line a baking sheet with parchment paper.
02 - Whisk together flour, sugar, poppy seeds, lemon zest, baking powder, baking soda, and salt in a large bowl.
03 - Add cold cubed butter to flour mixture. Cut in using pastry blender or fingertips until mixture resembles coarse crumbs.
04 - Whisk together heavy cream, egg, lemon juice, and vanilla extract in a separate bowl.
05 - Pour wet ingredients into dry ingredients. Stir until just combined. Do not overmix.
06 - Turn dough onto lightly floured surface. Gently knead a few times, then pat into 1-inch thick circle (about 7 inches wide).
07 - Cut dough into 8 wedges and transfer to prepared baking sheet, spacing slightly apart.
08 - Brush tops with extra heavy cream.
09 - Bake for 16-18 minutes or until golden brown. Transfer to wire rack to cool.
10 - Whisk powdered sugar with lemon juice until smooth. Drizzle over cooled scones before serving.