1. Preheat your oven to 220°C and put a large saucepan of water with a pinch of salt on to boil for the potatoes. Halve, peel and chop the onion into roughly 1cm pieces. Peel and grate the garlic(or use a garlic press). Chop the mushrooms into roughly 1cm pieces. Separate the broccoli into florets. Peel and chop both types of potato into roughly 2cm cubes.
2. Heat a glug of oil in a large pan on medium heat. Add the onion and cook until soft, 4 mins. Add the garlic and mushrooms and rosemary (if using). Cook for 3 mins more. Then add the lentils and vegetable stock. Season with a pinch of salt and a good grind of black pepper.
3. After a few minutes, add the tomato purée, diced tomatoes and Worcestershire sauce. Bring to the boil then reduce the heat and simmer until thickened, about 30 mins, or until lentils are fully cooked.
4. Meanwhile, add both types of potato to the boiling water and cook for 15-20 mins. TIP: The potatoes are cooked when you can easily slip a knife through. Once cooked, drain in a colander. Put them back in the pan and add the butter along with a pinch of salt and some black pepper. Mash until smooth.
5. Transfer lentil mixture to an ovenproof dish, spread the mash on top and grate over the cheese (if using). Pop on the top shelf of your oven and bake until golden, 15-20 mins.
6. Put the broccoli on a baking tray and drizzle over some oil. Season with salt and black pepper. Once the cottage pie has been in your oven for 5 mins, put the broccoli on the middle shelf and roast until the edges are crispy and slightly charred, 10-15 mins.
7. Once it's golden brown, serve on plates with a portion of roasted broccoli on the side.

Serve and enjoy!