Preheat oven to 425F. Line two baking sheets with parchment paper and set aside. In a large bowl, combine flour, baking powder, baking soda, salt, and sugar. Using a pastry cutter or a fork, cut in cold butter until mixture is crumbly.
In a separate bowl, whisk sour cream, lemon juice, zest, egg, half-and-half, and vanilla until smooth. Pour over dry ingredients, add poppyseeds and gently stir until a dough forms.
Scoop dough by 1/4 cupfuls and place 2-in apart on prepared baking sheets. Bake scones at 425F 12-15 minutes until golden-brown. Cool on a wire cooling rack.