Preheat your oven to 200C/Fan 180C/Gas mark 6.
Trim and rinse the leeks clean under a cold tap. Chop the leeks into rough 1cm rounds. Peel the garlic cloves and crush or finely grate. Pick the rosemary leaves and finely chop. Scrub the beetroot clean and coarsely grate.
Pour 2 tbsp oil into a large, oven proof pan and bring to a medium heat. Slide in the chopped leek, garlic and rosemary. Sprinkle in a generous pinch of salt and pepper and fry for 6-8 mins, stirring occasionally, till softened.
Turn the heat up slightly and stir in the risotto rice. Grate in the lemon zest. cook for 1-2 mins, stirring frequently, till the rice starts making a popping sound.
Slide the beetroot into the pan and pour in 2 ltrs of boiling water. Crumble in the stock cube and stir well till dissolved. Bring to the boil.
Pop a lid on the pan and slide it into the oven. Cook for 30 mins, stirring 2 or 3 times during that time.
While the risotto is cooking, trim any thick, dry leaves away from the spinach. Roughly shred the leaves. When the risotto is ready and the rice is tender, remove from the oven and stir in the spinach for 1-2 mins, till wilted. Squeeze in the lemon juice and have a taste of the rice. Add a little more salt and pepper if needed.
Ladle the risotto into bowls and serve.