Pull the leaves and silks off the sweetcorn cobs. Stand the cobs upright on a board. Run a knife down them to slice off the kernels. Chuck the kernels in a pan with a pinch of salt. Set aside.
Peel and chop the onion. Warm ½ tbsp oil in a deep frying pan or wok over a low heat. Add the onion. Season with salt and pepper. Fry for 5-8 mins till soft, stirring often.
While the onion cooks, halve the peppers. Scoop out the seeds and white bits. Roughly chop the peppers. Peel and crush the garlic. Roughly chop the tomatoes.
Add the peppers to the frying pan. Fry for 3-4 mins till they start to soften. Add the garlic, tomatoes, half the olives and half the thyme leaves. Cook over a high heat for 3 mins, then turn the heat down and gently cook for 10 mins till thick.This is your peperonata.
Pour 200ml boiling water over the sweetcorn kernels. Cover. Put on a high heat. Bring to the boil. Turn the heat down and simmer for 5 mins. Drain the sweetcorn over a jug so you save the cooking water. Return the sweetcorn to the pan. Add the butter to the sweetcorn.
Use a hand-held blender to blitz the sweetcorn with 50ml of the cooking water to make a rough purée. No blender? Ladle the corn into a food processor with a little cooking water and pulse till you get the consistency you want. Or, mash the corn in a bowl with a masher – you won’t need to add extra water. Taste and season. Gently reheat over a low heat till hot. Add a little more cooking water if it’s too thick. Cover and set aside.
Shred the lettuce. Mix it with the rest of the olives. Drizzle over ½ tbsp oil and toss to mix. Spoon the sweetcorn polenta into two bowls. Top with the peperonata and the rest of the thyme leaves. Serve with the salad.