Heat the oven to 160 C / 320 F. Spread the almonds on a sheet pan 33 x 46 cm / 13 x 18 inch and toast for 8 to 10 minutes, until fragrant and lightly colored. Cool completely, then chop roughly, keeping some pieces whole for texture.

Lower the oven to 150 C / 300 F and line the same sheet pan with fresh parchment.

In a large mixing bowl, whisk the egg whites with a hand mixer until foamy, about 1 minute. Add the sugar gradually and keep whisking until you get a loose, glossy meringue that holds soft peaks, 3 to 4 minutes. Don't push past soft peaks or the dough turns airy instead of dense.

Fold in the flour, cinnamon, lemon zest and salt with a spatula until just combined.

Fold in the chopped toasted almonds. The dough will be thick, sticky and heavy with nuts.

Wet your hands lightly and shape tablespoons of dough into short logs about 8 cm / 3 inches long. Pinch and flatten each end slightly so it looks like a knobby bone. Place on the sheet pan, spacing them 5 cm / 2 inches apart.

Bake for 25 to 30 minutes, until pale gold and firm to the touch, with a few natural cracks across the surface.

Turn off the oven and leave the cookies inside with the door propped open for 15 to 20 minutes. This second drying step is what gives Oss de Mòrd di Lanzada their bone-hard bite, skip it and they stay chewy.

Transfer to a wire rack and cool completely, they'll firm up further as they cool.

Dust with powdered sugar just before serving, if using.