Melt the butter in a large skillet over medium heat. Add in the onions and cook, stirring regularly, until the onions are light brown and have caramelized. (This process may take 20-30 minutes. Just keep stirring. Just keep stirring.).
Remove the onions from the heat and allow to cool to room temperature.
Once the onions have cooled, add in the neufchatel, sour cream and yogurt. Season with salt and pepper.
Refrigerate until ready to serve; serve with chips, carrots, celery or whatever you'd like.