NOTE : When I don't have mirin in stock at home, I use "apple syrup". Dilute it five times with water.
1.Making the beef topping
In a cooking pot, add all the seasoning ingredients for the beef, and start to cook over medium-high heat. Just before it boils, add the beef. Cook the beef, stirring occasionally. Once it has boiled, turn the heat to low and simmer for 5 min. Set aside.
2.Making the udon soup
In a big cooking pot, add 2L water and katsuo dashi pack (optional, if manage to get some). Turn the heat to high. Just before it boils, add all the soup ingredients (soy sauce, mirin, sugar, salt and dashi powder) and bring it to a boil. Remove the dashi pack powder from the soup. Set aside.
3. In another large pot, bring water to a boil over high heat. Add the udon and cook until just softish (or the hardness you like of course). Drain and split the udon noodles in each large serving bowl. Pour the hot udon soup form #2 over the noodles.
4. Top with the cooked beef and sprinkle some of sliced scallions over the beef. Serve immediately!
In Europe it is a bit difficult to find thinly sliced beef. So I usually purchase a whole cut of beef, then I freeze it and slice it myself. These days I love to use "Basse Cote à Braiser" for this dish.