Prepare blistered shishito sauce up to 5 days in advance. In a cast iron pan over high heat add shishito peppers to a tablespoon of oil, cook without stirring until beginning to blister, about a minute. Add sliced onion slices and stir fry until peppers are blistered, about 3-4 minutes. Then set aside and allow to cool slightly before cutting the stems off. Add cooled, stemmed blistered shishitos a food processor or high-powered blender with remaining sauce ingredients and process until smoot...
