Line a large baking tray with parchment paper.
In a large mixing bowl, whisk together the egg whites, ground almonds, sugar and almond extract at medium speed of your electric mixer for three minutes. Let it sit for 5 minutes.
Then transfer the batter to a piping bag with a 1cm round tip and pipe circles onto the lined baking tray. Press one almond into the center of the piped batter.
Cover loosely with foil and let it sit at room temperature overnight.
Bake at a preheated 350°F/180°C for 12-15 minutes. Let it cool slightly in the tray before transferring to a wire rack to cool completely. If the Amaretti is still sticking to the tray, bake for an additional 2 minutes.