Everything simmers in a single pan until the orzo turns silky and the tomatoes collapse into a light, glossy sauce. Weeknight dinner, minimal washing up.
Warm the olive oil in a wide, deep pan over medium heat. Soften the onion with a pinch of salt for 6-7 minutes, then add the garlic and tomato puree and cook for 1 minute more.
Stir in the orzo, then pour in the hot stock. Simmer, stirring often so it does not catch, for 10-12 minutes until the orzo is tender and the liquid has thickened to a glossy sauce.
Add the tomatoes and cook for 5 minutes, pressing them with a spoon until they slump and release their juices.
Off the heat, beat in half the Parmesan and most of the basil. Season to taste.
Serve in bowls topped with the remaining Parmesan, the last of the basil and a thread of olive oil.