Scrape the cod roe from its membrane.
Boil the udon noodles in boiling water, then rinse them in cold water.
Melt the butter in a pan and sauté minced garlic.
Add the cod roe and stir-fry lightly.
Add the udon noodles and mix quickly.
Pour in milk and soy sauce, and simmer until thickened.
Transfer to a bowl, sprinkle with chopped green onion, and serve.