Preheat oven to 350°F. Line baking sheets with parchment paper and set aside.
In a small bowl, combine flour, baking soda, baking powder and salt. Whisk together to combine.
In the bowl of a hand of stand mixer, fitted with a paddle attachment, cream the butter and sugar together until light and fluffy, 2-3 minutes. Add in the egg yolk, lemon zest, lemon juice, and vanilla, mix again until fully combined.
Add in the dry ingredients and mix on low until incorporated, scrape down the sides if needed. Add in the poppy seeds and gently mix in. The dough will be slightly sticky to the touch.
Transfer the dough out onto a clean, lightly floured surface. Roll out to about 1/2" thick. Using a cookie cutter, cut the dough into shapes. Re-roll the remaining dough and continue cutting until all dough is used.* If desired coat the unbaked cookies in coarse sugar before baking.
Arrange the cookies on the prepared baking sheets, about 2" apart. Chill for 30 minutes.
Once chilled, remove from the fridge and bake at 350 for 4-6 minutes.* Allow to cool for 4-5 minutes on the baking sheets before transferring to a cooling rack. Enjoy immediately or keep in an airtight container for 3-4 days.
Notes
*It doesn’t seem like a lot of dough, but you get a lot of cookies from the dough scraps you re-roll, you can also scoop this dough with a portion scoop.*Baking time is dependent on the size of the cookies, I would start with 4-6 minutes and increase baking time as needed.