Preheat the oven to 190-200ºc.
Cut the peppers in half, pull out the stems and deseed them. Place cut side up on a roasting tray* (see notes) and sprinkle with chopped rosemary and thyme. Drizzle with olive oil and toss with the chopped onion and peeled garlic. Sprinkle over the brown sugar. Roast in the preheated oven for about 15 minutes, until peppers are soft and charred on the edges.
Once the peppers, onions, and garlic are softened and charred on the edges, place them in a medium saucepan and pour in 500ml vegetable stock made from a stock cube dissolved in boiling water.
Use an immersion blender to blend the soup until thick and smooth. Once the soup is blended add in the basil leaves. No need to chop the basil at all, just toss in whole leaves and blend again until the basil has been blended into the soup. Taste and adjust the seasoning. Just be careful with the salt as the stock cubes are very well seasoned.
Add in the juice of ½ a lemon to lift the smokiness of the soup and compliment the basil.