Step 1: Prepare the Spinach

If using fresh spinach, wash it thoroughly under cold water to remove dirt. Chop it into smaller pieces for easier blending later. Steam the spinach in a pot over medium heat until wilted, then drain excess liquid by pressing it against a colander or squeezing it with paper towels. If using frozen spinach, ensure it’s fully thawed and squeezed dry.

Step 2: Sauté the Aromatics

Heat olive oil in a skillet over medium heat. Add the diced onion and sauté for about 3 minutes, stirring occasionally, until translucent. Toss in the minced garlic and cook for another minute, ensuring it doesn’t burn. Remove from heat and set aside.

Step 3: Combine Ingredients

In a large mixing bowl, combine the sour cream, mayonnaise, shredded mozzarella, and grated Parmesan. Stir well to create a smooth base. Fold in the cooked spinach and sautéed onions and garlic. Season with salt, black pepper, and cayenne pepper if desired. Mix everything thoroughly so all flavors meld together.

Step 4: Bake the Dip

Preheat your oven to 375°F (190°C). Transfer the mixture to an oven-safe baking dish, spreading it evenly. Sprinkle additional mozzarella or Parmesan on top for a golden crust. Bake for 20–25 minutes, or until bubbly and slightly browned around the edges.

Step 5: Serve Warm

Let the dip cool for a few minutes before garnishing with fresh parsley or red pepper flakes. Serve immediately while still warm.