Prepare the washed leek by removing the tough 1-2 outer layers and chopping off the root at the end and the tough green tops. Slice in half lengthways, and then again, so you end up with 2 long strips. Slice these strips across so you end up with lots of little squares.
Heat the oil in a large, heavy-bottomed pan. Add the leek and cook for 3-4 minutes, stirring every so often until it is soft, but not brown. Meanwhile, boil the kettle – you’ll need a large mugful of hot water.
Add the rice, tinned tomatoes, tomato purree and salt and give everything a good stir. Cover and cook for about 20-25 minutes – give it a stir every 5 minutes or so and check it isn’t dry – depending on your rice and pan you may need to add in more water.
When the rice is cooked and tender, stir in the spinach and dill. Serve with a chunk of lemon on the side to squeeze over at the table.