Drain the cannellini beans in a colander and rinse with fresh water. Cut the olives into halves or quarters. Set aside.
Place the tahini, lemon juice and garlic in the bowl of the food processor. Process until very smooth, about 1-2 minutes. Add the olives to the food processor and process until smooth.
Next add the beans, 1/3 of them at a time, processing until smooth after each addition. After processing the first 1/3 of the beans, add 2 tbsp cold water and puree. Then continue with the second and third portions of the beans. Scrape down the sides of the bowl with a rubber spatula as needed.
Finally, add 2 tbsp. olive oil and blend well. If the hummus is too thick, add a tiny bit of ice water, 1 tablespoon at a time until desired consistency. Usually, given the liquid from the olives, you won’t need to add any added liquid.
To serve, spoon the mixture into a flat bowl. Using the back of a spoon, make little canals in the hummus by starting on the outside of the bowl and working your way to the center of the bowl. Drizzle the remaining olive oil in the cavities and garnish with minced parsley.