Place the chickpeas in a small saucepan and add just enough water to cover them, stir in the baking soda and then bring to a boil. Simmer for 20 minutes.
Put the garlic, salt and lemon juice in a food processor or blender and blitz until the garlic is finely chopped. Leave to mellow.
Drain the chickpeas. Add the tahini to the food processor and blend for 30 seconds, add ice water. Next add chickpeas and everything else.
Blend until smooth. Scrape the mix from the sides down into the blender to make sure nothing gets missed, and blend again until everything is silky smooth.