- 5 tablespoons unsalted butter
- 2 tablespoons vegetable oil
- 1 red onion, thinly sliced
- 1 yellow onion, thinly sliced
- Kosher salt and cracked black pepper
- 1 cup mayonnaise
- 3/4 cup sour cream
- 4 ounces cream cheese, softened
- 1/2 teaspoon cayenne pepper
- One 10-ounce box frozen spinach, thawed and drained
Melt the butter in a large skillet over medium heat and add the oil. Stir in the onions and sprinkle liberally with salt and pepper. Reduce the heat to medium-low and cook the onions, stirring occasionally, until caramelized, 30 minutes. Remove from the heat and cool.
Combine the mayonnaise, sour cream, cream cheese and cayenne in a mixing bowl and mix vigorously until smooth. Add the onions and thawed and drained spinach and mix well. Taste and adjust the seasoning with salt and pepper as necessary.