Cut open the mentaiko and extract the contents, reserving a small portion for topping.

Place the frozen udon noodles on a microwave-safe plate, cover loosely with plastic wrap, and heat according to the package instructions.

In a bowl, whisk the tofu until smooth, then add the milk, grated cheese, and white dashi. Mix well to create the tofu cream.

Heat the tofu cream in a pot over medium heat, stirring until it starts to simmer. Lower the heat and add the mentaiko and butter, mixing well. Add the udon noodles and coat them with the tofu cream.