In a pot, lay in the kelp and put in potatoes, corn, and just enough dashi to cover them. Bring to a simmer over medium heat. Skim off the foam when it rises on the surface.
Lower the heat and continue to simmer with a small lid directly on the potatoes (you can substitute with aluminum foil cut into the size of inner pan) until slightly softened but still crisp (for about 10 mins).
Add sugar, soy sauce and then turn off the heat. Let it cool.
Remove the kelp and simmer uncovered until the liquid is almost gone over medium heat. Add butter and mix.
Place in a serving plate and top with blanched green beans and pepper.