In a small bowl or jar, whisk everything together. The mustard should help it emulsify, coming together as a thick dressing that’s no longer separated. (If you use a jar, you can put the lid on and just shake it.)
Using a large salad bowl, add the kale and about 1/4 cup of this dressing. Mix thoroughly and refrigerate until you’re ready to eat (about 10 minutes or several hours both work great).
Serve with the remaining dressing. Add shredded carrots, cucumbers, celery, tomatoes, or any other toppings your family enjoys.
Store any remaining dressing in the fridge for about 2 weeks.