Preheat the oven to 350 degrees F.
Prepare 2 rimmed baking sheets with parchment paper.
Using a hand-held mixer, beat together the egg whites and salt in a medium bowl on medium speed until soft peaks form, about 2 minutes.
Sprinkle in the granulated sugar and continue to beat until very soft peaks form, another 2 minutes.
Add the almond flour, slivered almonds, Citron and lemon zest and use a rubber spatula to stir and fold until just combined.
Scoop heaping 1 tablespoon mounds onto the prepared baking sheets.
Bake, rotating the trays halfway through, until lightly brown on the edges, about 25 minutes.
Remove and allow to cool for 10 minutes on the tray.
Dust with the confectioners' sugar and serve.