In a large bowl, combine 8 cups of cold water, the chickpeas and 2 tablespoons of the salt. Let soak at least 12 hours, or overnight. 

In a large stockpot over high, bring another 10 cups of water and the baking soda to a boil.

Drain the soaked chickpeas, discarding soaking water, and add to the pot.

Return to a simmer, then reduce to medium and cook until the skins are falling off and the chickpeas are very tender, 45 to 50 minutes. 

Set a mesh strainer over a large bowl and drain the chickpeas into it; reserve ¾ cup of the chickpea cooking water.

Let sit for 1 minute to let all liquid drain. Set aside about 2 tablespoons of chickpeas, then transfer the rest to the food processor. Add the remaining 1 teaspoon of salt, then process for 3 minutes.

Stop the processor and add the tahini. Continue to process until the mixture has lightened and is very smooth, about 1 minute.

Use a rubber spatula to scrape the sides and bottom of the processor bowl. With the machine running, add the ¾ cup of cooking liquid and the lemon juice.

Process until combined. Taste and season with salt.

Transfer the hummus to a shallow serving bowl and use a large spoon to make a swirled well in the center.

Drizzle with olive oil, then top with the reserved 2 tablespoons chickpeas, parsley, cumin and paprika.