Ingredients

• 2 tablespoons vegetable oil
• 1 medium onion, finely chopped
• Kosher salt
• 8 ounces cream cheese, room temperature
• 1/2 cup mayonnaise
• 2 teaspoons cornstarch
• 4 ounces sharp white cheddar, coarsely grated (about 1 cup), divided
• 2 ounces Monterey Jack, coarsely grated (about 1/2 cup), divided
• Freshly ground black pepper
• 2 tablespoons finely chopped chives
• 2 tablespoons finely chopped peperoncini
• Crackers and/or tortilla chips (for serving)

Instructions

1. Preheat oven to 375°. Heat oil in a medium skillet over medium. Cook onion, stirring occasionally, until golden brown and softened, 8–10 minutes; season with salt. Let cool.
2. Pulse cream cheese and mayonnaise in a food processor until smooth.
3. Toss cornstarch, 3/4 cup cheddar, and 1/4 cup Monterey Jack in a medium bowl to coat cheese. Mix in cream cheese mixture and cooked onion; season with salt and pepper. Scrape into a 1-qt. baking dish and top with remaining cheddar and Monterey Jack. Bake dip until golden and bubbling, 20–25 minutes. Let dip cool 5 minutes, then top with chives and peperoncini. Serve with crackers.