Preheat the oven to 425 degrees and line 2 baking sheets with parchment paper.

Add the potatoes to a stock pot and cover with water. Place on the stove and bring to a boil. Boil for 15-20 minutes or until the potatoes are fork tender. Drain and allow to cool for a few minutes.

Add some oil to both baking sheets. Evenly split the potatoes between the baking sheets. Use the bottom of a glass cup to flatten the potatoes. To each baking sheet add half of the oil and half of the dry seasonings. Place in the oven for 20 minutes. Remove from the oven, flip the potatoes and place back in the oven for 20 more minutes – be sure to alternate the racks the baking sheets were on.

Meanwhile, add the mayo, celery, green onions, garlic, apple cider vinegar and mustard to a large bowl. Mix until combined and set aside.

Remove the potatoes from the oven and allow to cool for 5 minutes. Roughly chop the potatoes and add them to the bowl with the dressing (reserving a few for topping). Toss until coated, taste and adjust the seasonings if needed. Top with the reserved potatoes.

Serve at room temperature or chilled.