Preheat your oven to 350°F (175°C). Line two baking sheets with parchment paper.
In a large bowl, cream together butter, granulated sugar, and brown sugar until light and fluffy (about 2–3 minutes).
Add the egg, lemon zest, lemon juice, and lemon extract (if using). Beat until fully combined.
In a separate bowl, whisk together flour, baking soda, salt, and poppy seeds.
Gradually mix the dry ingredients into the wet until just combined. Avoid overmixing.
Chill the dough for 15 minutes if it's very soft or your kitchen is warm.
Scoop dough balls using a tablespoon or cookie scoop. Place on baking sheets about 2 inches apart.
Bake for 9–11 minutes, until edges are lightly golden and centers still look soft.
Cool on the baking sheet for 5 minutes, then transfer to a wire rack.
(Optional) Whisk powdered sugar and lemon juice to make a glaze. Drizzle over cooled cookies.