Line 2 baking sheets with nonstick baking paper. Whisk the egg whites in a clean bowl with a hand-held electric whisk until they form stiff peaks. Mix together the sugar, ground almonds and salt in a bowl, then fold gently into the egg whites with the almond extract.
Sift the icing sugar into a separate bowl. Roll the almond mixture into 22–24 walnut-sized balls, then roll them in the icing sugar to coat. Place on the prepared baking sheets and push 1 blanched almond, if using, gently into each.
Bake in a preheated oven, 180°C (350°F), Gas Mark 4, for 15–18 minutes, or until cracked and pale golden. Transfer to wire racks to cool slightly.
Scoop the ice cream into 6 espresso cups or heatproof glasses and pour 1 shot of strong, hot coffee over each. Serve immediately with the amaretti biscuits.