Place the chickpeas, garlic (if using - see notes) and the baking soda in a medium saucepan. Cover the chickpeas by several inches of water, then bring the mixture to a boil over high heat. Continue boiling, reducing heat if necessary to prevent overflow, for about 15 minutes.
Remove the garlic (if using). In a fine-mesh strainer, drain the chickpeas and run cool water over them for about 30 seconds. Set aside.
Meanwhile, in a food processor or high-powered blender, combine tahini and lemon juice, and blend until a fine paste forms.
Add the cooked chickpeas and blend for at least 1 minute, drizzle with 2 to 3 tablespoons of ice water, blend for another minute, add garlic, salt and 2 tablespoons of ice water and blend for another minute. Scrape down the food processor or blender, and blend some more if necessary, until the mixture is ultra smooth, pale and creamy.
Taste and adjust salt if necessary. Scrape the hummus into a serving bowl or platter. Top with garnishes of your choice, and serve. Leftover hummus keeps well in the refrigerator, covered, for up to 1 week.