In the bowl of a stand mixer, fitted with the paddle attachment cream together the butter, sugar, and salt.
Scrape the bottom and sides of the bowl. Add the egg and vanilla, beat until combined.
Add the flour and baking powder, mix until well blended.
Add the lemon juice and zest and mix well. Form dough into a disk, wrap with plastic wrap and chill for at least 30 minutes.
While dough is chilling, prepare the glaze by whisking the powdered sugar, lemon juice, and vanilla bean seeds, salt, and hot water in a small mixing bowl. Reserve.
Preheat the oven to 350°F. Line a cookie sheet with parchment paper.
On a lightly floured surface, roll out the dough till 1/4 inch thick. Punch with your favorite small cookie cutter, I used an Ateco daisy cutter.
Bake for 10-12 minutes and allow to cool. For the glaze, mix all ingredients together.
After cookies have cooled completely, dip the cookies into the glaze and place on a rack for glaze to harden.