Place the tomatoes, onions, and whole garlic cloves on a large roasting tray. Drizzle with the olive oil and add sprinkle with salt and pepper to taste.
Toss to coat and bake for 40 minutes.
Allow the vegetables to cool slightly before peeling away the skin from the garlic cloves and adding everything to a large blender along with the vegetable stock, heavy cream, and basil.
Blitz until completely smooth, and add some extra seasoning to taste if desired.
Serve, optionally with extra cream and basil leaves as garnish.