For the hummus, first simmer the chickpeas over low heat for 120 minutes with the lid closed until very soft.
Drain, retaining a little cooking liquid, blend finely in a hand blender. Pour in garlic, juice of one lemon, tahina and enough olive oil to create a smooth, almost creamy consistency. Add a little cooking liquid if necessary. Allow to cool.
Drizzle the hummus with a little olive oil, garnish with parsley and serve.