If you have a hard time finding onion powder (not the same as onion salt), feel free to use crushed dehydrated onion flakes. Just add to taste.

2 tablespoons extra virgin olive oil
2 large yellow onions (about 1 1/2 pounds), finely chopped
3/4 cup sour cream (low-fat is fine if you like)
3/4 cup Greek yogurt (low-fat is fine if you like)
3 teaspoons dehydrated onion powder/granulates (salt-free, natural)
very scant 1/2 teaspoon salt

In a large thick-bottomed skillet over medium heat saute the chopped onions in the olive oil along with a couple pinches of salt. Stir occasionally with a wood or metal spatula and cook until the onions are deeply golden, brown, and caramelized - roughly 40 or 50 minutes (see photo at website). Set aside and let cool.

In the meantime, whisk together the sour cream, yogurt, onion powder, and salt. The important thing is to add whatever onion powder you are using to taste. Add a bit at a time until it tastes really good. Set aside until the caramelized onions have cooled to room temperature. Stir in 2/3 of the caramelized onions, scoop into a serving bowl, and top with the remaining onions. I think this dip is best at room temperature.

Makes about 2 cups.

Caramelized Onion Dip Recipe - 101 Cookbooks