- 1/4 cup unsalted butter
- 2 onions, thinly sliced
- 2 cloves garlic, minced
- 1/4 teaspoon dried thyme
- Kosher salt and freshly ground black pepper, to taste
- 1/4 cup beef broth
- 1 tablespoon red wine, optional
- 4 ounces cream cheese, at room temperature
- 1/4 cup sour cream
- 3 tablespoons mayonnaise
- 1 cup shredded mozzarella cheese, divided
- 2 tablespoons freshly grated Parmesan
- 2 tablespoons chopped fresh parsley leaves
- Preheat oven to 350 degrees F. Lightly oil a 9-inch baking dish or coat with nonstick spray.
- Melt butter in a large skillet over medium high heat. Add onions, garlic and thyme; season with salt and pepper, to taste. Cook, stirring occasionally, until the onions are very soft and caramelized, about 25 minutes.
- Stir in beef broth and red wine, if using. Bring to a simmer; remove from heat and stir in cream cheese, sour cream, mayonnaise, 1/2 cup mozzarella and Parmesan.
- Spread mixture into the prepared baking dish; sprinkle with remaining 1/2 cup mozzarella. Place into oven and bake until bubbly and golden, about 10-12 minutes.
- Serve immediately.