Melt the butter in a large skillet over medium heat. Allow it to foam, then stir in the chopped onions with a generous pinch of kosher salt and pepper. Cook for 5 minutes until the onions start to soften.

Reduce the heat to low and cook the onions, stirring often, for 30 to 60 minutes until they turn dark brown and caramelized.

Cool the caramelized onions slightly before mixing them into the dip base. You can prepare the onions ahead of time and keep them refrigerated.

Whisk together the sour cream, mayonnaise, garlic powder, and a good pinch of salt and pepper in a bowl. Stir the caramelized onions into the mixture.

Taste the dip and adjust seasoning if needed, adding more salt or pepper to your liking.

Serve the dip with chips, crackers, pretzels, or fresh veggies. Garnish with freshly chopped parsley if desired.