Heat oven to 220C/200C Fan/Gas Mark 7. Place peeled and cubed sweet potatoes and carrots on a large roasting tin and drizzle with oil and plenty of seasoning.
Roast the vegetables in the oven for 25-30 minutes or until tender and caramelised.
Meanwhile fry the finely chopped onions in a deep saucepan over a medium heat for 10 minutes or until softened.
Add the crushed garlic cloves and stir for 1 minute. Then add the stock. Simmer for 5-10 minutes until the onions are very soft then set aside.
Once the roasted vegetables have done and cooled a little transfer them to the saucepan and blend all the ingredients till smooth. Season and serve.