Preheat your oven to 350 degrees Fahrenheit (175 degrees Celsius). Line two large baking sheets with parchment paper and have a piping bag fitted with a round tip (size 12 or 1/2 inch) ready.

In a large, scrupulously clean bowl, begin beating 5 egg whites with a pinch of salt on medium-high speed until stiff, glossy peaks form, about 3 to 4 minutes.

Sift together 2 cups ground almonds, 1 1/2 cups powdered sugar, and cardamom or 1/2 teaspoon ground cardamom into a separate bowl.

Gently fold the almond mixture into the whipped egg whites in two additions, keeping as much air in the batter as possible.

Spoon the batter into your piping bag filled about two-thirds full.

Starting with the largest ring, pipe a 5-inch diameter circle of batter onto the prepared baking sheet. Then pipe smaller rings about 0.5 inches smaller each time until about 18 to 20 rings are piped ranging from 5 inches down to about 1 inch across. Space rings about 1 inch apart.

Bake the rings for 35 to 40 minutes until pale golden and edges feel slightly firm. Avoid overbaking to prevent brittleness.

Remove baking sheets from oven and cool rings on sheets for about 5 minutes. Then transfer rings to wire racks and let cool completely for about 30 minutes.

Prepare royal icing by whisking 2 egg whites with 2 cups powdered sugar and 1 tablespoon lemon juice on low speed for about 1 minute.

Gradually add 1 to 2 tablespoons water, a teaspoon at a time, until a thick, spreadable consistency that holds peaks but flows slightly when piped is reached.

Place the largest ring on a flat serving plate. Pipe a thin line of royal icing around the inside edge, then place the next smaller ring directly on top, centering it carefully.

Repeat icing and stacking with all remaining rings, working from largest to smallest, building a tall tower.

Optionally, insert a thin wooden dowel or skewer vertically through the center before stacking for stability, removing it gently once icing sets.