If using fresh spinach, wash thoroughly and remove thick stems. Bring a large pot of water to a boil and blanch the spinach for 30 seconds to 1 minute until wilted. Drain immediately and transfer to a bowl of ice water to stop cooking. Squeeze out as much liquid as possible using your hands or a clean kitchen towel, then coarsely chop. If using frozen spinach, thaw completely and squeeze out all excess water, then coarsely chop. You should end up with about 1 1/2 cups packed chopped spinach from 10 oz fresh or equivalent frozen.

Sauté aromatics

Heat olive oil and butter in a skillet over medium heat until the butter melts and foams. Add the finely chopped onion and sauté until soft and translucent, about 5–7 minutes. Add the minced garlic and cook for 30–45 seconds more until fragrant, taking care not to brown the garlic.

Combine spinach and aromatics

Add the well-drained chopped spinach to the skillet and cook with the onions and garlic for 1–2 minutes to meld flavors and evaporate any remaining moisture. Remove from heat and let cool for 3–5 minutes.

Mix base and cheeses

In a large bowl, combine the cream cheese (or creamed cottage cheese), sour cream, and mayonnaise. Beat or stir until smooth. Stir in the grated Parmesan and shredded mozzarella until evenly incorporated.

Season and finish

Add the cooled spinach mixture to the bowl with the cream base. Stir to combine. Add lemon juice, salt, black pepper, and red pepper flakes (if using). If the dip seems too thick, stir in up to 2 tablespoons cream to reach desired consistency. Taste and adjust seasoning. Fold in chopped fresh dill or parsley if using.

Optional: Bake for warm dip

Preheat the oven to 375°F (190°C). Transfer the dip to an oven-safe baking dish (about 1-quart). Smooth the top and sprinkle an additional 2 tablespoons mozzarella and 1 tablespoon Parmesan over the surface. Bake for 12–15 minutes until hot and bubbly and the top is lightly golden. For a browned top, place under the broiler for 1–2 minutes, watching carefully.

Serve

If serving chilled, refrigerate for at least 30 minutes to allow flavors to meld, then bring to room temperature before serving. If baked, serve hot straight from the oven. Garnish with a sprinkle of chopped herbs and a grind of black pepper.

To Serve

Arrange toasted baguette slices, crostini, and raw vegetables on a platter. Provide a small serving bowl or serve the baked dish directly from the baking dish. Dip with bread or vegetables.