In the bowl of a stand mixer fitted with the whisk attachment, beat the 5 egg whites for 1 minute to combine. Add the cream of tartar and continue beating the whites on high speed until soft peaks form, 3 to 5 minutes. Add the scraped vanilla bean seeds and continue beating until it is fully incorporated and the whites are glossy, 2 to 3 minutes. Remove the bowl from the mixer and use a rubber spatula to gently fold in the lemon zest and the powdered sugar mixture.
Coat 1 or 2 large baking sheets with a layer of parchment paper. Spray the paper with a thin layer of nonstick spray. Put heaping teaspoonfuls of the batter about 2-inches apart on the tray(s). Take care to leave the space between each mound because this batter spreads as it bakes.
Put the tray in the center of the oven and bake for 8 minutes, then raise the temperature to 375 degrees F and bake until the cookies are golden brown around the edges and form a nice shell-like exterior, about 10 to 12 minutes. Remove from the oven and allow them to cool for a few minutes before gingerly removing them from the tray with an offset spatula. Take care! They can stick to the paper.
Recipe courtesy Alex Guarnaschelli