Whisk the egg whites to stiff peaks in a clean bowl, then whisk in the almond extract and lemon zest.

In a separate bowl, sift together the icing sugar, ground almonds and a pinch of salt. Gently fold this into the whisked egg whites until it all comes together into a dough. Cover and chill for at least 4 hrs, or ideally overnight.

Heat the oven to 190C/170C fan/ gas 5. Turn the dough out onto a work surface generously dusted with icing sugar. Roll into a long, fat sausage (about 40cm long) and cut 2cm-thick slices down the length (you should get about 20). Shape each slice into an oval and pat down the tops a little – the biscuits should be about 4-5cm wide and 5-6cm long. Arrange on a baking tray lined with baking parchment and dust with more icing sugar.

Bake for 20-23 mins until the biscuits are just turning brown. They will be soft, but will firm up as they cool. Leave to cool completely on the tray. Will keep in an airtight container for up to three days.