how to puree celery
Bring milk, water and celery root to a simmer in a large saucepan over medium heat. Reduce the heat to maintain a gentle simmer and cook until very tender, about 30 minutes. Reserve 1 cup of the cooking liquid, then drain. Puree the celery root, butter, salt and pepper in a food processor (or blender) until smooth and the consistency of thinned mashed potatoes.