Preheat the oven to 165°F. Lightly grease (or line with parchment) two baking sheets.
In a small bowl, whisk together the masa harina and flour. Set aside.
In a medium bowl, beat together the butter, confectioners sugar, salt
and lemon zest at medium-high speed until very smooth and creamy, about 5 minutes.
Stop to scrape down the sides of the bowl as needed.
Stir in the vanilla and lemon paste.
Add the dry ingredients, mixing on low speed until the dough comes together.
Portion the dough into 1 1/2" balls; a level tablespoon cookie scoop works well here.
Gently roll the dough balls in granulated sugar to coat before placing onto the prepared baking sheets.
Use a fork to lightly flatten the top of each cookie once.
Bake the cookies for 12 to 16 minutes, or until they're set and the edges are starting to brown slightly.
Remove the cookies from the oven and allow them to cool right on the baking sheet; they're quite fragile when warm. Cool completely before serving.
Store cookies, well wrapped, at room temperature for several days; freeze for longer storage.