Trim off the leaves of the cauliflower and cut the white part into small pieces. Cook in boiling water until soft. Drain. Use a blender to puree the cooked cauliflower. If too dry, add some broth or milk. Mix cauliflower puree and broth in a pot, boil then turn down the heat and simmer for 15 minutes. Add milk and salt to taste, adjust the seasoning to your liking. Turn off the heat and add egg yolks. Stir to combine. Ladle soup into bowls, and garnish with green onions. Place some tobiko in the center.