Put the milk and cashews in a blender and process into a smooth cream. Set aside.
Put the rutabaga, carrots, and parsnips in a large saucepan. Cover with water and bring to a boil over medium-high heat. Decrease the heat to medium and cook until the vegetables break apart easily with a fork, 30–45 minutes. Drain and return the vegetables to the saucepan.
Add the cashew cream, nu