Basil Pesto Pasta with Blistered Tomatoes

Bring 4 litres of water to a rolling boil in a large pot. While it heats, toast the cashews in a dry frying pan over medium heat for 3 to 4 minutes, shaking often, until pale golden. Tip them onto a plate to cool.

Pick the basil leaves from the stems and pat them dry. Put the basil, cooled nuts, garlic and Parmesan in a food processor and pulse until coarsely chopped.

With the machine running, pour in the olive oil in a steady stream. Add the lemon juice, a pinch of salt and some pepper, then blend until the pesto is thick and spoonable but still slightly textured. Taste and adjust the seasoning.

Add 1 tablespoon of salt to the boiling water, then the spaghetti. Cook for 1 minute less than the packet time, until just firm to the bite (al dente). Stir in the first minute so it does not stick.

While the pasta cooks, heat 1 tablespoon of olive oil in a large frying pan over high heat. Add the tomatoes cut side down and cook for 3 to 4 minutes, until the skins blister and the edges soften. Season lightly and turn off the heat.

Scoop out a mug (about 250 ml) of pasta water, then drain the spaghetti.

Return the pasta to the warm pot, off the heat. Add the pesto and 4 tablespoons of pasta water, and toss until every strand is glossy and coated. Add more water a spoonful at a time if it looks tight.

Fold in the blistered tomatoes and their juices. Serve straight away with extra Parmesan and black pepper.