Trim bottom of celery stalks by cutting off the base. Trim tops and wash really well. Save tender inner stalks for another use. Peel the celery strings with a vegetable peeler. Cut stalks in half crosswise
Place in pot that just fits celery in one layer.
Add dashi, olive oil and a salt to taste (remembering that the dashi is lightly salty). Take a piece of parchment paper and cover and tuck in celery with it.
Bring dashi to a boil. Cover pot with lid and lower heat so that the broth simmers. Cook until celery is tender when pierced with a paring knife. Let the celery cool to room temperature in the broth or chill until ready to serve.
When ready to serve carefully lift the celery out of the broth and place on serving plate. Pour excess broth into measuring cup.
Vinaigrette and Finishing
Whisk broth and sesame oil together. Pour over celery. Grate hard boiled egg over dressed celery. Garnish with celery seeds.
Dashi
Put water and kombu together in small pot. Let kombu soak for 15 minutes.
Bring kombu and water to a point just below boiling. Add bonito flakes and let steep until they fall to the bottom of the pot, about 10 minutes. Do not stir. It will cloud the broth.
Strain mixture through a coffee filter set into a sieve. It should be a clear straw color.