Pre-heat your oven to 180C Fan/200C/400F/Gas Mark 6
Peel and deseed the squash, then cut it into chunks. Toss the squash in little oil and with the sage, then roast it on a baking tray in the oven for 25-30 minutes until it is soft
Warm the vegetable oil in a pot on a low heat, add the onion and garlic, and cook for around 5 minutes until soft
Add the chopped tomatoes, tomato puree, vegetable stock, sugar and water. Bring it to a gentle simmer for 10 minutes
Then, take off the heat and add the roasted squash to the mixture. Use a stick blender to puree the soup
Add the salt to taste, then you can also add more water too at this point if you'd like a thinner soup
Serve warm, or allow to fully cool and store in the fridge or freezer for later use