3 Tbsp. extra-virgin olive oil
3 Tbsp. unsalted butter
1 large, sweet onion (Vidalia), diced thin (about 2 cups)
1 medium-size yellow onion, thinly diced (about 2 cups)
1 medium-size red onion, thinly diced (about 2 cups)
3 medium shallots, thinly sliced (about 3/4 cup)
1/2 tsp salt, plus more to taste
6 scallions, thinly sliced
8 ounces cream cheese, softened
1 1/2 cups sour cream
1/4 cup mayonnaise
2 tsp garlic powder
1/4 tsp cayenne pepper
Black pepper, to taste
Potato chips, toasted bread, and seasonal vegetables, for serving. (We love salt and vinegar chips)
1 Heat oil and butter in a large, deep skillet over medium-high until butter melts.
2 Add all of the thinly sliced onions (NOT scallions yet), and salt; cook, stirring occasionally until barely softened and just starting to brown, about 12 minutes.
3 Reduce heat to medium-low. Cook, stirring occasionally, until onions are caramelized, about 35 minutes, adding scallions halfway through cook time. If onions start to stick to skillet or brown too quickly, add a splash of water to the skillet.
4 Transfer mixture to a large bowl, and place cream cheese on top; let cool completely, about 30 minutes.
5 Stir onion mixture until cream cheese is fully incorporated. Add sour cream, mayonnaise, garlic powder, and cayenne to onion mixture; stir well to combine. Season with salt and black pepper to taste.
6 Cover and chill at least 3 hours or up to 8 hours or overnight.
7 Let dip stand at room temperature 30 minutes before serving.
8 Dip can be made up to 1 day ahead and stored in an airtight container in refrigerator.