The night before you intend to make the hummus, put chickpeas in a bowl and cover with 3-4 quarts of water. Soak chickpeas at room temperature overnight. In the summer, keep the bowl in the refrigerator.
The next day, drain chickpeas, cover with about 4 inches of water, add baking soda, and bring to boil over medium high heat. Skim foam with a large spoon, lower heat, cover and cook for about 1.5 hours, stirring occasionally (this will help remove the skins), until chickpeas are very soft and almost falling apart. Remove skins if they float to top.
When chickpeas are cooked, turn off the heat and keep on the stove so it stays warm.
To make tahini sauce: Mix tahini, lemon juice, cold water, salt and cumin with a fork or a whisk until smooth. You might have to add more water or tahini if it doesn't get smooth. A dd some water, one tablespoon at a time and blend until smooth. If it's too watery, add tahini, one tablespoon at a time and blend until it reaches the right texture. (Note: This sauce is great on its own on bread or as a dressing!)
Move about 1/2 cup of the ready tahini sauce to a bowl.
Add about 1/2 cup of the warm chickpeas using a skimmer on top of the tahini sauce.
Quickly mash the mixture with a potato masher or a fork, until most of the chickpeas are mashed.
Top with olive oil and your favorite toppings. Enjoy with pita, bread or on its own.