Preheat the oven to 350°F. Line baking sheets with parchment paper or silicone baking mats. Set aside.

In a medium bowl, whisk together the flour, baking soda, baking powder, and salt. Set aside.

In the bowl of a stand mixer fitted with the paddle attachment or in a large bowl with an electric hand mixer, cream the butter and sugar together on medium speed until light and fluffy, about 3-5 minutes, scraping down the sides of the bowl as needed.

Add the egg and mix until well combined. Scrape down the sides of the bowl. Add the lemon zest and lemon juice and mix until combined, again scraping the sides of the bowl.

Slowly add the dry ingredients until just combined. Add the poppy seeds and mix on low speed until distributed through the dough.

Using a small (1 tablespoon) cookie scoop, scoop the dough onto the prepared baking sheets, leaving 2 inches between the cookies. Bake for 9-11 minutes, or until the bottom edges of the cookies just barely start to turn golden.

Allow the cookies to cool on the baking sheets for 5 minutes before transferring them to a wire rack to finish cooling.

Once cooled, whisk the glaze ingredients together until smooth. Dip the tops of the cookies in the glaze, allowing the excess to drip off or using the side of the bowl to remove excess glaze. Allow the glaze to set before serving.