Preheat the oven to 170c/325f. Line two baking trays with a silicone mat or baking parchment.
Using a hand whisk or mixer, whisk the egg whites to stiff peaks. Fold in the ground almonds, caster sugar, Amaretto, 1 tsp of the cinnamon and the vanilla extract.
Place the caster sugar and icing sugar for rolling on two separate plates. Using a teaspoon or your fingers, scoop out a chunk of the cookie mixture and roll it into a ball in your hands (about the size of a walnut). Roll it in the caster sugar, then roll it in the icing sugar and place on the baking tray.
Repeat with the remaining dough until you've used it all up. Leave a bit of space between the cookie balls as they will expand slightly during cooking.
Use your finger to squash the cookie balls a little, then place in the oven to cook for 15 minutes.
Take out of the oven, leave to cool for 5 minutes then sprinkle with the remaining cinnamon. Serve them warm, or allow to cool completely on the tray.
Recipe by at https://www.ideahacks.com/cinnamon-amaretti/