Fill your kettle and boil it. Fill a large pan with the hot water, topping it up if needed, and add a pinch of salt. Cover and bring the water back to the boil. Meanwhile, peel and finely chop the onion.

Preheat your grill to high. Warm a large frying pan on a medium heat. When warm, add ½ tbsp olive oil, the onion and a pinch of salt and pepper. Fry, stirring, for 5 mins, till the onion has just started to soften and brown.

The water in the pan should be boiling by now. Add the gnocchetti and simmer for 8 mins, till the pasta is tender but still has a little bite. Meanwhile, halve the cherry tomatoes.

Stir the cherry tomatoes into the onion with 2 tbsp cold water. Cook for 3-4 mins, stirring once or twice, till the tomatoes start to soften. While the tomatoes cook, peel and finely chop or grate the garlic. Finely chop the chilli, scraping out the seeds and white pith if you prefer less heat. Rinse 1 tbsp capers with cold water (they can be salty).

Stir the garlic, chilli and capers into the tomatoes and add 100ml cold water. Cook, stirring every so often, for 5 mins, till the tomatoes have broken down to a chunky sauce. Meanwhile, drain the mozzarella and tear it into small pieces.

Stir the baby leaf spinach into the tomatoes to wilt it. When the pasta is cooked, drain it and stir it into the tomatoes. Taste and add a little salt or pepper if you think it needs it.

If your frying pan is ovenproof, scatter the mozzarella over the pasta and slide it under the grill. Otherwise, transfer the pasta and sauce to an ovenproof dish, top with the mozzarella and slide under the grill. Cook for 2-3 mins till the cheese is melted and golden. Serve the gratin in 2 warm bowls, drizzled with a little olive oil if you like.