Bring a large pot of water to boil. Simmer walnuts for 5 minutes. Drain, do not rinse. Pat the warm walnuts dry and transfer to a bowl. Sprinkle with sugar and gently toss to coast. Spread in single layer on rimmed baking sheet and allow to sit uncovered overnight.
Heat oil in a wok or heavy bottom pot, fry walnuts in batches until golden brown. Remove with slotted spoon onto a small mesh rack over a foiled line baking sheet. Sprinkle with sesame seeds. Allow walnuts to cool completely. Store up to two weeks in an air-tight container.
This recipe requires an overnight (or at least 8 hour) resting period before flash frying.