Preheat the oven to 400°F (200°C) and line a baking sheet with parchment paper.
In a bowl, combine the flour, poppy seeds, sugar, salt, and baking soda. Set aside.
Grate the frozen butter using the side of a box grater with large holes.
Cut the grated butter into the dry ingredients using a pastry cutter, fork, or your hands until the mixture resembles a coarse meal with pea-sized pieces of butter.
In a small bowl, whisk together the egg, vanilla extract, lemon zest, lemon juice, and milk. Optionally, reserve 1 tablespoon of the mixture to use as an egg wash later.
Add the wet ingredients to the butter and flour mixture and bring the dough together. Do not knead it—just press and squeeze it with your hands until it forms a cohesive dough.
Transfer the dough onto a floured surface and shape it into a 2-inch (5cm) thick disk. Cut it into 8 triangles and place them on the prepared baking sheet.
Bake for 15-18 minutes or until golden on top and around the edges.
Allow the scones to cool to room temperature before glazing.
To prepare the glaze, combine all the icing ingredients in a bowl. Adjust the lemon juice as needed to achieve a thick but pourable consistency.
Pour the glaze over the scones or dip the tops into the glaze, shake off the excess, and place them on parchment paper to set.