Soak the chickpeas in a quart of water overnight. Drain and place in the pot with a fresh quart of water and the baking soda. Bring to a boil, and then simmer for an hour or till creamy. Drain, reserving the liquid.
Assemble ingredients as cooked chickpeas cool.
Mix 1/4 cup of the reserved chickpea cooking liquid with the lemon juice. This may seem to curdle.
Whisk 2 tablespoons of the olive oil with the tahini.
Process the chickpeas, garlic, salt and cumin in a food processor for about 15 seconds. Scrape sides.
With processor running, add the lemon mixture slowly through the feed tube. Process for about a minute. Scrape down.
Slowly add the tahini mixture through feed tube as processor runs.
Process till smooth and creamy. Allow to sit for a half hour for flavors to blend.