While fries are soaking, make the hummus. Add chickpeas and tahini to a food processor and pulse until finely chopped. Add the lemon juice, garlic, harissa, and salt. With the motor running, stream in the olive oil and let it whirl until super creamy. Set aside. Heat a heavy stock pot fitted with a deep-fry thermometer with oil to 325℉.
Raise heat of oil to 350℉. Cook potatoes again, 2 handfuls at a time, until golden brown, 1-2 minutes. Remove from oil, shake off excess oil, drain on paper towels or rack, and immediately season with salt. Repeat until all potatoes are cooked.