1. Warm your oven to 200°C/Fan 180°C/Gas 6. Peel the potatoes. Slice them into chips about 1cm-thick and slide them into a large pan. Cover the chips with cold water and pop the pan on the hob. Bring the pan to the boil, then reduce to a gentle simmer. Cook the chips for 5-6 mins, then drain well.
2. Meanwhile, halve the aubergines and score a crosscross onto the cut side of each half. Arrange the aubergines, cut-side-up, in a roasting tin. Drizzle the aubergines with oil and season with salt and pepper. Slide the aubergines into the oven and roast for 40 mins.
3. As soon as the aubergines go into the oven, pour 2 tbsp oil into a separate, large roasting tin and add a pinch of salt and pepper. Slide the tin onto a shelf below the aubergines and warm up for 5 mins. When the tin is hot, remove it from the oven. Carefully add the drained chips to the tin and use a spatula to turn them in the oil. Slide the chips into the oven and bake for 40 mins, turning halfway, till golden and crisp.
4. While the aubergines roast, make your piri piri sauce. Trim the tops off 4 chillies and roughly chop them, removing the white pith if you prefer less heat. Peel and roughly chop the garlic cloves. Pick the thyme leaves. Add the chillies, garlic and thyme to a small food processor.
5. Squeeze in the juice from both lemons and pour in 50ml red wine vinegar. Spoon in 1 tbsp smoked paprika, 1 tsp dried oregano and 1 tbsp sugar. Season with a pinch of salt and pepper and turn on the processor. Whizz the sauce until well combined and smooth, then pour into a small bowl. No processor? Finely chop the chillies and thyme leaves, grate or crush the garlic, and mix with the remaining ingredients to make a chunkier sauce.
6. When the aubergines have roasted for 40 mins, remove the tin from the oven. Spoon most of the piri piri sauce over the aubergines (save a few spoonfuls for serving) and use a brush to evenly distribute it. Slide the aubergines back into the oven and roast for a further 10 mins.
7. Transfer the cooked aubergines to a platter. Serve with the chips and remaining piri piri sauce on the side, for dipping, and your favourite sides and salads.