In a skillet, melt the butter over medium heat. Add the chopped onions and cook until they are caramelized and golden brown, stirring occasionally. This may take about 20-25 minutes.
Let the onions cool, then combine them in a bowl with sour cream, mayonnaise, and Worcestershire sauce.
Mix until well combined.
Notes
Be patient while sautéing the onions. It takes time to caramelize them and develop the sweet flavor.
Keep the heat medium-low while caramelizing the onions to prevent them from burning.
Make sure to stir the onions occasionally for even browning.
If your dip is too thick, you can thin it out with a little milk or cream.
This dip tastes better when refrigerated for a few hours before serving, as the flavors get more time to blend together.