Preheat the oven to 400℉.
First, remove the skin from the sweet potatoes then cut the potato into small cubes. In a large bowl, add oil, salt and pepper to the potatoes. Give them a toss.
Then, bake on a non-stick sheet pan or one lined with parchment paper for 45 minutes in the preheated oven. Once, done remove the sheet pan and allow the sweet potatoes to cool.
While baking make the dressing. Put together mayo, mustard, honey, rosemary and apple cider vinegar. Give everything a good mix.
Now, dice the red onion and mince the celery.
Once the sweet potatoes are cool add everything together in a large bowl. Be careful and fold everything in easily. You do not want to smash all the sweet potatoes.
Lastly, taste for salt and pepper before serving.