Preheat oven to 400F. Line 2 rimmed baking sheets with parchment.
Combine the flour, sugar, baking powder and salt in a large mixing bowl. Add the grated butter, and toss to incorporate. Stir in the egg, buttermilk, and 1 tablespoon vanilla extract until just combined, and be careful not to overmix. Fold in the blueberries and half of the lemon zest.
Turn the dough onto a lightly floured surface and gently pat it into a square about 1 inch thick. Slice the dough into 12 squares, then arrange them onto the baking sheets about 2 inches apart. Brush the scones with more buttermilk.
Bake 15-18 minutes, rotating the baking sheets after 8 minutes, until the scones are golden brown.
In a small bowl, whisk together the powdered sugar, lemon juice, melted butter and 1/2 teaspoon vanilla extract. Stir in the remaining lemon zest and the poppy seeds.
Let the scones cool a few minutes, then glaze with spoonfuls of lemon poppy seed glaze. Serve while still warm.