Wash potatoes in cold water and pat dry with a clean dish towel or paper towels.
Combine garlic salt, celery salt, onion powder, lemon pepper, and black pepper in a small bowl.
Place potatoes on a large, rimmed cookie sheet or stoneware pan. Stick each potato with a fork, about halfway through. Drizzle with olive oil and sprinkle with 1 teaspoon of the seasoning mix.
Bake for 15 minutes. Stir. Bake for an additional 10 minutes. Remove from oven.
While potatoes bake, place onion and celery in a food processor and pulse to chop as finely as possible. Combine onion and celery with mayonnaise, yellow mustard, and 1 teaspoon of the seasoning mix. Set aside.
Serve roasted baby potatoes with mayonnaise mixture. Potatoes are delicious when served hot, room temperature, or cold.
NOTE: This dressing/sauce can be made in advance but must be kept refrigerated until just before serving.
Keyword appetizer, charcuterie, potato, potatoes, recipe, salad, side dish, summer