Bring a large pot of well-salted water to a boil. Place the basil in a heatproof colander. Once the water is boiling, submerge the colander with the basil into the pot and use a spoon to push the leaves3 cups into the water. Blanch for 10 seconds, then immediately rinse the leaves under cold water to stop the cooking. Squeeze them dry with your hands. Reserve the boiling water.