Place the tomatoes, skin facing down, on a large baking sheet. Cut the tips off the garlic bulbs and place the garlic on the same baking sheet. Season the vegetables with salt and pepper, and drizzle a generous amount of olive oil on top. Cover the tray with foil and bake in the oven for 40 to 45 minutes. Remove from the oven and allow to cool.
In a medium size pot, sauté the onions in butter on medium heat until they have caramelised and have developed a golden colour. This will take about 15 to 20 minutes. Add the roasted tomatoes, the flesh of the roasted garlic, and any extra liquid from the baking sheet. Add the chicken stock and bring the liquid to a boil. If you want to add any other aromatics, now would be the time. You can use oregano, thyme, or basil if you want to add a little more. Blend the ingredients together with a hand blender until it has a smooth consistency. Add the cooking cream, adjust the seasoning with salt and pepper, and mix.