Put a large pan of salted water on to boil. Trim the roots and any woody greens off the leek. Halve it and rinse out any grit, then finely slice it. Trim the carrot, then peel it and dice it. Trim the dry ends off the celery and dice it too.

Put a deep frying pan or medium pan on a medium and add 1 tbsp olive oil and the chopped veg. Season with a pinch of salt and pepper and cook, stirring often, for 5 mins till the veg start to look glossy.

While the veg fry, tear any large mushrooms in half. Peel and crush or grate 1 garlic clove. Stir the mushrooms and garlic into the veg. Fry, stirring often, for 5 mins till mushrooms look juicy.

Drain the lentils, rinse them under cold water and tip them into the pan. Tip in the chopped tomatoes. Half fill the tin with around 200ml cold water and add that to the pan. Give it all a good stir, pop on a lid (or use a baking tray if you don't have a lid), then bring to the boil. When the sauce is boiling, turn the heat down and simmer for 15 mins, stirring every so often, till the sauce has started to thicken.

While the sauce cooks, peel and finely chop the other garlic clove. Slide it into a small bowl. Finely grate in the lemon zest. Pick the rosemary leaves off their woody sprigs and finely chop them. Add to the bowl. Squeeze in the juice from half the lemon and add 1 tbsp olive oil and a pinch of salt and pepper. Stir to mix – this is your gremolata.

When the sauce has 10 mins cooking time left, check the pan of water – it should be boiling. Add the spaghetti and simmer for 8-10 mins till it’s cooked but not too soft, it should still have a little bounce and bite to it.

Taste the bolognese sauce and add a pinch more salt or pepper if you think it needs it. Drain the spaghetti and toss with the bolognese sauce to coat, then heap onto 2 warm plates. Spoon over the lemon and rosemary gremolata and serve.