Whisk together ingredients for the vinaigrette until fully combined. Toss the kale in the dressing and season with salt and pepper to taste. Let sit for 10 to 15 minutes so the kale can soak in flavor.
Top with onion and hazelnuts before serving.
Notes
Pro tip: Make extra dressing and keep it for future use. If kept in a tightly sealed container it can be kept in the cupboard for a very long time.