In a bowl whisk together yogurt, sugar, lemon zest and juice, vanilla and poppy seeds. Let sit for 1 minutes to allow sugar to dissolve.
Add salt, baking soda and a third of the flour, stirring to combine. Add another third of the flour and stir again to incorporate. Add the final third of the flour and stir to incorporate. A soft dough will form.
Cover dough and place in the refrigerator for at least 4 hours or overnight. Chilling allows the dough to firm up.
After dough has chilled, preheat oven to 350 degrees. Line a baking sheet with parchment paper.
Scoop about a tablespoon of dough and roll into a ball. Place on prepared baking sheet. Continue rolling dough into balls and place several inches apart on baking sheet.
Gently flatten balls using the palm of your hand to form a cookie shape. Sprinkle with additional poppyseeds, if desired.
Bake for 11-14 minutes until edges are set and the bottoms are lightly golden. Allow to cool on pan for a few minutes before transferring to a cooling rack.
Store in an airtight container for 3-4 days.