In a large skillet, melt the butter over medium heat.

Add the sliced onions and salt, stirring occasionally until they are soft and caramelized, about 15 minutes.

Once the onions are nicely caramelized, sprinkle in the black pepper and garlic powder.

In a mixing bowl, combine the softened cream cheese and sour cream.

Add the shredded cheddar and grated Parmesan cheese to your cream mixture.

Fold the sautéed onions into the cheese mixture, ensuring everything is well combined.

Stir in the Worcestershire sauce.

Pour the mixture into an oven-safe baking dish.

Preheat your oven to 350°F (175°C) and bake the dip for 20-25 minutes until bubbly and golden on top.