Heat the oil in a large saucepan and cook the onion over a medium heat for 7–8 minutes until softened. Add the garlic and cook gently for a further 2 minutes until softened.
Pour the passata and chickpeas into the pan with the hot stock, then bring to the boil and simmer gently for 15 minutes until rich and thickened slightly.
Add the basil leaves, reserving a few for garnish. Season to taste, then blend with a hand-held blender until smooth and thick, adding a little extra water for the desired consistency. (Don't worry if you do not have a blender; this soup can be served as a chunky version.)
Ladle into warmed mugs to serve and garnish with the reserved basil leaves.