For the hummus: Spread the chickpeas out on a baking sheet and comb through to rid them of pebbles, little clumps of earth-anything that is not a chickpea.
Wash well in several changes of water, and drain. Transfer to a large bowl with 4 cups water. Stir in the baking soda and let the chickpeas soak overnight, at least 12 hours and up to 24 hours.
Drain the chickpeas and wash in a couple changes of fresh water to rinse off the now-soapy soaking liquid.
Bring the chickpeas and 6 cups water to a boil in a medium saucepan over medium-high heat. Boil for 2 or 3 minutes, then reduce the heat to low and gently simmer, uncovered, until the chickpeas are very soft, verging on mushy, about 40 minutes. Start checking for doneness at the 30 minute mark. Thanks to their baking soda bath, the chickpeas will throw off copious amounts of foam during cooking. Skim, skim, and keep skimming. You'll want to remove as much foam as possible.
Drain the chickpeas, transfer to a food processor, and process into a smooth paste, scraping down the bowl with a rubber spatula as needed. With the machine running, add the tahini, lemon juice, salt and garlic. Give them a minute to whirl about, and then slowly drizzle in the ice water. Process for at least 5 minutes, and feel free to process longer. This final stage is absolutely key to getting the smooth, creamy, whipped quality you're looking for.
At this stage, the hummus will be quite warm and considerably looser than you are probably accustomed to. Do not worry; these are signs of good things to come.
Taste for seasoning and acid balance, and add more salt, lemon or tahini to taste. You're looking for an equilibrium, such that the mixture doesn't so much taste of garlic, or tahini, or even chickpeas; it tastes of hummus, a thing far greater than the sum of its parts.
For the tahini sauce: Combine 1/3 cup water, the tahini, lemon juice and a couple pinches salt in a small bowl, and beat with a fork to blend. The mixture will thicken dramatically. Thin with more water, as needed. The sauce should have the consistency of heavy cream. Beat in the lemon zest.
For assembly: Spoon 3 or 4 large dollops of hummus into a wide, shallow bowl (a pasta dish is ideal). Spread the hummus in an even layer across the base of the bowl by rotating it around the back of a serving spoon, leaving a well in the center of the hummus. Pour a liberal amount of olive oil around the edges, enough to form a sort of green moat. Drizzle 1 or 2 tablespoons of the tahini sauce over the hummus. Sprinkle with healthy pinches of cumin, paprika and chopped parsley.
Serve with warm pita and pickles.
NotesCook's Note: If you are not going to consume the hummus immediately--though I strongly suggest you do; if you've never tried warm hummus, you're in for a treat--transfer the hummus to a bowl and cover the surface with plastic wrap. Leave the hummus to rest at room temperature for 30 minutes or as long as 2 hours. Some people enjoy hummus immediately, the moment it's made. Others prefer it after it's had an hour or two for its flavors to develop. The choice is entirely yours. Just know that hummus becomes much heavier as it sits and cools, with the garlic coming to the forefront and the lemon growing increasingly muted. Any leftover hummus will keep in the refrigerator for up to 3 days.