Soak wooden skewers in a shallow tray of cold water for 30 minutes.

Cut lamb shoulder into 1 cm cubes. Keep fat-bearing pieces separate so you can alternate them during threading.

Thread each skewer tightly: 2 lean cubes, 1 fat cube, 2 lean cubes, 1 fat cube, continuing until you have 8-10 pieces per skewer with no gaps between them.

Lay threaded skewers on a tray. Refrigerate uncovered for up to 8 hours, or proceed immediately.

Light charcoal in a chimney starter and let it burn until all coals are fully white-ashed, about 20-25 minutes. Pour coals into the base of the grill and spread evenly into a single dense layer.

Set the grill grate as close to the coals as possible, about 5-7 cm above the embers. Let it preheat for 5 minutes until it's too hot to hold your hand near for more than 2 seconds.

Remove skewers from the fridge and season all sides lightly with coarse sea salt right before grilling.

Place skewers on the hot grate in a single layer. They should sizzle loudly on contact.

Turn skewers every 30 seconds using tongs, rotating a quarter turn each time. Total cook time is 4-5 minutes. Look for a golden-brown char on all four sides of each cube with visible grill marks.

Check doneness: lamb should read 63 C / 145 F on an instant-read thermometer for medium, or 70 C / 158 F for well-done, which is the Abruzzese preference.

Transfer to a board or wrap loosely in foil. Rest for 1 minute, then drizzle with olive oil if using. Serve immediately.