Remove frozen udon from package. If you are using other type of udon noodle, then cook according to package instructions
Add butter on top of udon noodle
Heat in microwave for 2 minutes or until hot and butter is melted
Remove mentaiko from sac/ membrane
In a separate bowl, combine sauce ingredients
Once udon noodles are done, pour the sauce over udon
Mix well
Add optional toppings
Serve hot and enjoy!