1. In a large cooking pot, add water (2L) and bring it to a boil, add "katsuodashi pack" if you have and simmer for about 5 min. Remove it from the water.
2. Add all the soup ingredients and bring it to a boil. Set aside.
3.Make the tenkasu In a small bowl, add flour, salt and water. Mix well. In a small cooking pot, add about 2 to 3 cm of oil and when the temperature reaches about 160℃, sprinkle the tenkasu batter, using a egg whisk.
4. Deep-fry until they are lightly browned. Transfer onto the paper towl to remove excess oil.
5. In a big cooking pot, add water and bring it to a boil. Add the soba noodles, and stir gently, so they don’t stick together. Cook until al dente or how hard you like your soba.
6. Drain the soba noodles and wash the noodles in cold water to get rid of any slimy texture.
7. Then put the soba noodles into the boiling water to warm up again. Once they are warm, drain well and place them into a serving bowl.
8. Pour the soup and sprinkle sliced leek as much as you want and then "Tenkasu".