Heat olive oil in a medium skillet over medium heat until shimmering
Add onion and ¼ tsp of the salt
Sauté (stirring frequently) until medium brown and caramelized (apx 20-25 minutes)
Transfer the caramelized onions to a small mixing bowl and return pan to heat - Reduce heat to medium-low
Use a micro plane grater to grate the garlic into the pan (a garlic press or minced is too 'chunky' you want it basically a purée) - Sauté (stirring constantly) until raw smell is gone (apx 2 minutes) - Transfer to the mixing bowl with the onions - Allow to cool for 10 minutes
After 10 minutes, whisk in the sour cream, mayonnaise, white pepper, the remaining ½ tsp of kosher salt, and the powdered celery seed (if using) until everything is well mixed and distributed
Cover and chill in the refrigerator for a minimum 1 hour to allow the flavors to develop
Give it a good stir just before serving
Serve with assorted 'dipping vegetables', crackers, potato chips, toasted pita wedges, pretzels, etc, etc... You know what a dip is for!