Heat the oil in a roasting pan large enough to take the vegetables in one layer.
Place the onions and carrots in the roasting pan and turn carefully in the hot oil.
Season with salt and black pepper.
Add the bay leaves and thyme to the pan and roast, turning occasionally, for 30-45 minutes or until the vegetables are tender and beginning to caramelize.
Transfer to a large saucepan.
Add the stock to the pan and bring to the boil.
Reduce the heat and simmer for a further 10-15 minutes.
Remove the herbs and liquidize the soup.
Strain back into the rinsed-out pan and return to the boil.