Preheat oven to 400°F. Line a baking sheet with parchment paper.

In a medium bowl, combine sugar and lemon zest; mix with your fingertips until the sugar is moistened and fragrant. Add in the flour, baking powder, baking soda, salt and poppy seeds and mix until combined.

Grate butter into flour mixture on the large holes of a box grater; use your fingers to work in the butter until the mixture resembles coarse crumbs.

In a small bowl, whisk the sour cream, lemon juice, egg and vanilla until smooth.

Using a fork, stir sour cream mixture into flour mixture until large dough clumps form. Use your hands to press the dough against the bowl into a ball. The dough will be dry, then sticky, but as you press, the dough will come together.

Place on a lightly floured surface and pat into a 7-inch circle about 3/4-inch thick. Use a sharp knife or bench scraper to cut into 8 triangles. Place on the prepared baking sheet, about 1 inch apart. Bake until golden, about 15 to 16 minutes. Cool for 10 minutes and prepare the glaze.

In a medium bowl, prepare the glaze by mixing together the melted butter, powdered sugar, vanilla and lemon juice. Whisk until smooth. Dip the top of the scones into the glaze and allow the glaze to harden.