Preheat the oven to 425°F. In a large bowl, combine flour, sugar, baking soda, baking powder, and salt.
Work the butter into the flour mixture using hands or a pastry cutter until it resembles fine breadcrumbs.
Add the vanilla seeds and lemon zest and combine into the flour.
Make a well in the center of the mixture, and pour in the buttermilk and vanilla extract.
Combine until everything is moistened, but do not knead the dough. This is the most important step. If you overwork your dough, the scones will be tough, not tender and light.
Turn the mixture out onto a floured surface.
Gather the dough together and pat it into a rectangular shape that is about 1 1/2 inches thick. Cut the scones into 12 wedges.
Place scones on a baking sheet lined with parchment paper. Brush with heavy cream and sprinkle with sanding sugar.
Bake for about 12 minutes.