Preheat oven to 375°F (190°C). Position rack in center for even browning. This temperature ensures the dip heats through while developing a golden, bubbly top.

Cook bacon in a large skillet over medium heat until crispy, about 8-10 minutes. Reserve 2 tablespoons of bacon fat for cooking spinach. Drain bacon on paper towels and chop into bite-sized pieces when cool.

If using frozen spinach, thaw completely and squeeze in a clean kitchen towel until absolutely no water remains - this is crucial for preventing watery dip. For fresh spinach, sauté in reserved bacon fat until wilted, then squeeze dry. The spinach should feel almost dry and compressed.

In a large bowl, beat softened cream cheese with an electric mixer until fluffy and smooth. Mix in mayonnaise and sour cream until the mixture is completely smooth with no lumps visible. The base should be creamy and well-combined.

Stir in minced garlic, smoked paprika, garlic powder, and cayenne pepper (if using). Season with salt and pepper to taste. The mixture should smell aromatic and well-seasoned at this point.

Gently fold in the prepared spinach, 3/4 of the chopped bacon, 3/4 cup mozzarella, 3/4 cup cheddar, and 1/2 cup Parmesan cheese. Mix until evenly distributed. The texture should be thick but still spreadable.

Transfer mixture to a greased 10-inch cast iron skillet or 2-quart baking dish. Spread evenly and top with remaining mozzarella, cheddar, Parmesan, and bacon pieces. Drizzle lightly with olive oil to promote browning.

Bake for 25-30 minutes until edges bubble vigorously and top turns golden brown with darker spots. The center should jiggle slightly when shaken. For extra browning, broil for 2-3 minutes, watching carefully to prevent burning.

Let cool for 5 minutes before serving to prevent burns. Serve hot with tortilla chips, toasted baguette slices, crackers, or fresh vegetables. The dip will continue to thicken slightly as it cools.