Preheat the oven to 350°F. Combine the almond flour, all-purpose flour, baking soda, baking powder, and salt in a mixing bowl. Whisk to combine.
Add the butter and sugar to the bowl of a stand mixer fitted with a paddle attachment. Cream together on medium speed for about 3 minutes, or until light and smooth. Mix in the egg, vanilla, and almond extracts, scraping down the bowl as needed. Add the dry ingredients to the bowl. Mix to combine. Lastly, mix in the lemon zest and poppy seeds.
Pour the remaining ½ cup of sugar into a small bowl. Scoop a heaping tablespoon of cookie dough (about 1 ½ tablespoons) and form it into a tight ball. Roll the dough ball in the sugar to coat. Place it on a cookie sheet. Repeat with the remaining dough, spacing the cookies out so they have room to spread (you’ll need 2-3 cookie sheets for all of the dough).
Bake the cookies for 12 minutes on the middle rack. Let the cookies cool for 5 minutes on the cookie sheet. Use a metal spatula to transfer them to a cooling rack.
For the glaze, whisk together the powdered sugar, lemon juice, lemon zest, water, and almond extract until smooth.
When the cookies are fully cooled, dip them into the glaze or spoon the glaze over top. Immediately decorate with the sliced almonds and poppy seeds. Allow the glaze to set.