Start by making the mayonnaise.
Soak the cashews in hot water for 30 minutes to soften.
Drain the cashews and add to a high-speed blender along with all the other mayonnaise ingredients.
Blend at high speed until smooth and creamy.
Peel and cut the potatoes into 1” cubes, add to a large pot of cold water and bring to the boil. Reduce to a simmer and cook 15-20 minutes until just fork-tender. Once cooked, drain and rinse the potatoes under cold water for 1 minute to stop further cooking.
Add potatoes to a large bowl and add in the white vinegar and stir to coat the potatoes.
Add the celery and green onions to the potatoes.
To make the dressing, whisk together the cashew mayonnaise, yellow mustard, celery seed, salt and pepper.
Pour the dressing over the potato mixture and toss gently.
Add dill or paprika if desired.
Cover and chill in the fridge for 2 hours before serving.
