Beat egg whites on high speed until foamy and add the lemon juice. Continue beating until medium-stiff peaks form.
With the beaters on, gradually add the sugar and cinnamon and continue beating until glossy, stiff peaks form.
Remove about ½ cup of the mixture to another small bowl and set aside. (If baking cookies same day, they may stay uncovered at room temperature. Otherwise, cover tightly with plastic and refrigerate.)
To the remainder of the eggs, add the almond meal and mix to make a soft dough. Refrigerate dough for 1 hour (or a few days)
Preheat oven to 275 F
Sprinkle a sheet of parchment paper generously with powdered sugar and plop the dough onto it then sprinkle with more sugar and lay another sheet of paper on top. Pat out gently to about a ⅓ inch thick and cut into stars. Remove excess dough from around the stars and lift paper onto a baking sheet.
Transfer to greased cookie sheets and glaze with reserved meringue (from step 2). Garnish with slivered almonds if you like.
Bake for about 25-30 minutes until meringue top is set, but still white. Remove from oven and let cool completely on baking sheets.
Store airtight tins.