If using a slow cooker:
Add the dried chickpeas and baking soda to a large slow cooker. Add enough water to cover the chickpeas by at least 6 cm. Cover and cook until tender: high heat for 5 hours or low heat for 8 to 9 hours.
If using a pressure cooker:
Add the dried chickpeas and baking soda to a large pressure cooker. Add enough water to cover the chickpeas by at least 6 cm. Cook on high pressure for 45-50 minutes. Use the quick release method.
Hummus:
Place the cooked chickpeas, garlic, and kosher salt in the bowl of a food processor. Process for at least 30 seconds. Stop, scrape down the sides of the bowl, and process for at least another 30 seconds. Add the lemon juice and water. Process for 30 seconds. Add the tahini and process for 30 seconds, then scrape down the sides of the bowl.
With the processor running, drizzle in the olive oil and stop when oil has been incorporated.
To serve, transfer the hummus to a bowl and drizzle with additional olive oil and sprinkle with sumac, to taste, if desired.

Slow cooker/pressure cooker chickpeas

1 kg of dried chickpeas, sorted and rinsed
3/4 teaspoon baking soda

For the hummus

454g cooked chickpeas
10g minced garlic
10g salt
75ml lemon juice
60ml water, preferably chickpea cooking water
82g tahini, stirred well
54ml extra virgin olive oil, plus extra for serving
Powdered sumac: optional