Chop the negi/leek. (Don't toss the green part of the leek. We need it.）
Put oil in a non-stick skillet, and sauté the chopped leek over low to medium heat until they're cooked.
Combine miso, sugar, sake, grated ginger and white sesame paste. (If you don't like sweet tastes, reduce 2 tsp sugar. )
Add the miso mixture to the skillet. Keep stirring till it gets thick. Add white sesame and mix. Remove from heat and let it cool.
Sprinkle a little bit sesame seeds on the top.