In a food processor, combine rice vinegar, miso, mayonnaise, lemon juice, ginger and sugar and mix until smooth. Adding ¼ cup at a time, pour in olive oil and continue to process until fully emulsified, scraping down the sides as you go. Season with salt and pepper to taste and serve.
Notes
Storage: Dressing will keep well, sealed, in the fridge for up to 2 weeks.