Place the scrubbed potatoes in a large pot and cover them with cold water. Add 2 tsp of kosher salt. Bring the water to a boil and cook until the potatoes are fork-tender, about 15-20 minutes. Drain thoroughly and let them cool slightly so they can be handled.

Preheat your oven to 400°F (200°C) or set your air fryer to 380°F (195°C). Lightly toss the slightly cooled potatoes with 1 Tbsp of olive oil and a generous sprinkle of smoked paprika, salt, and pepper.

Carefully place the seasoned potatoes onto a parchment-lined baking sheet (or directly into the air fryer basket). Using the bottom of a sturdy mug or a potato masher, gently smash each potato until it is flattened to about 1/2 inch thickness, ensuring the edges remain somewhat intact for crisping.

Roast the smashed potatoes for 20-25 minutes in the oven, or air fry for 12-15 minutes, flipping halfway, until they are golden brown and crispy on the edges. Set aside to cool slightly.

While the potatoes crisp, prepare the dressing. In a medium bowl, whisk together the mayonnaise, Dijon mustard, and apple cider vinegar until smooth. Stir in the diced celery, minced red onion, and most of the chopped chives. Season with salt and pepper to taste.

Gently transfer the warm, crispy smashed potatoes to the bowl with the dressing. Fold everything together slowly so the potatoes maintain their crisp texture and don't break apart entirely. Taste and adjust seasoning if needed.

Transfer the salad to a serving dish, garnish with the remaining fresh chives, and serve immediately for maximum crispness, or chill for at least 30 minutes if a colder salad is preferred.