Preheat oven to 180°C /160°C fan-forced. Slice the aubergine lengthways into 1cm thick pieces. Sprinkle with salt. Let aubergine rest for 15 minutes to release its moisture. After this time, brush both sides with oil and roast in the oven for 15 – 20 minutes or until soft.
Season lamb or beef mince with salt and fry in a little oil until nice and browned. Remove from pan and set aside.
Using the same pan on medium heat, fry onions until soft. Add garlic and cook gently for 1-minute, followed by harrisa, cinnamon, allspice and mint. Add another splash of oil if needed to avoid spices drying out or burning.
After a minute or two when spices have become fragrant, squeeze in tomato paste. Stir continuously until the paste becomes dark and sticky. It’s important to keep the heat of the pan gentle so the flavour can develop slowly. This is a very important part of the recipe. Take your time.
Add tomatoes, beef stock and minced meat, bring to the boil, then cover with a lid and simmer for 45 minutes.
For the bechamel, melt butter in a saucepan over low heat. Add flour, cumin, sumac and a pinch of salt, then stir to form a paste. Slowly whisk in milk, making sure there are no lumps. Cook over medium heat until sauce thickens.
Using a 26cm x 17cm oven-proof dish, layer ingredients, starting with half of the meat sauce, then layer half the aubergine slices and top with 1/3 of the bechamel sauce. Repeat layers again, finishing with bechamel sauce.
Bake in oven at 190°C / 170°C fan forced for 30 – 40 minutes. Let moussaka stand for 10 minutes in a warm place before serving.