Using an electric mixer, cream together the butter and sugar until well combined and creamy. Scrape down the sides of the bowl.
Add the lemon zest and mix on low speed until combined.
Add the salt and almond extract and mix on low speed to combine, scraping down the sides of the bowl as needed.
Add the almond flour in 3 separate additions, mixing on low after each addition until combined. The dough will be crumbly at first, but continue to mix on low speed and it will come together. Once the dough begins to stick together (see photo in the post above), stop mixing.
Divide the dough in half. Shape each half first into a ball and then into a log that is 1 ½ inches in diameter and wrap in plastic wrap. You can roll the dough log a bit more after wrapping it in the plastic wrap to smooth it out. Refrigerate for at least 2 hours and up to 24 hours.
When you are ready to bake the cookies, preheat your oven to 350 degrees F. Line two baking sheets with parchment paper.
Using a sharp knife, cut the dough into ¼-inch thick slices. Place the cookies on the prepared baking sheets, spacing them about 1 inch apart. Bake for 7-10 minutes, until the cookies are barely golden on the edges and bottoms. Be very careful not to over-bake the cookies. If you are baking two pans of cookies at once, rotate the pans from top to bottom and front to back halfway through the baking time.
Let the cookies cool on the baking sheet for 10 minutes before transferring them to a wire rack to finish cooling. Store cooled cookies wrapped airtight at room temperature for up to 5 days or in the freezer for up to 3 months.