To make the dough, in a large mixing bowl, stir the almond flour, confectioners' sugar, cardamom, and salt together. WIth an electric mixer running, slowly add the egg whites and almond extract, mixing until a dough forms.
Transfer the dough to a double boiler and knead the dough for about 10 minutes, working it with your hands until the dough becomes almost too hot to comfortably work with. (For this step I mix the dough in the large mixing bowl I use for my stand mixer, and set this over a saucepan of simmering water)
Preheat the oven to 350 degrees F.
Allow the dough to cool a bit, prepping the molds while you wait: Spray them with a baking spray or brush with a neutral oil or softened butter, then dust with semolina or cornmeal.
Form the dough into logs about the thickness of a finger and arrange them in the molds.
Slide these into the oven and bake for about 10 minutes, or until light gold. Allow to cool before assembling (some peopple even freeze the rings for 24 hours at this point, which some believe enhances the texture).
To make the icing, whisk together the confectioners' sugar, egg whites, and lemon juice. Transfer this to a pastry bag fitted with a small tip.
To assemble, place the largest ring on your serving plate or cake stand, attaching it with a little of the icing. Pipe the icing over it in a curved zigzag manner, letting it form a decorative scalloped shape on the sides, then set the next largest ring on top. Repeat with the remaining rings, working biggest to smallest, until you reach the top.
If you have extra dough, just roll this into separate cookies and bake, then drizzle with melted, tempered chocolate later.