Thaw the frozen spinach in a colander or the microwave. Once thawed, press and squeeze out as much liquid as possible using clean hands or a thin kitchen towel—aim for about 1 to 1 1/2 cups of drained spinach. Drain the canned artichoke hearts thoroughly and pat dry; chop any large quarters into bite-sized pieces if needed.

Make the base

Soften and combine cheeses

In a large mixing bowl, beat the room-temperature cream cheese with a spatula or electric mixer until smooth. Add the sour cream and mayonnaise and mix until fully combined and creamy.

Add seasonings and cheeses

Stir in the minced garlic, lemon juice, Dijon mustard, Worcestershire sauce, salt, black pepper, and crushed red pepper flakes until evenly distributed. Fold in the grated Parmesan and shredded mozzarella (reserve extra mozzarella and Parmesan for topping).

Fold in vegetables

Gently fold the well-drained spinach and chopped artichoke hearts into the cheese mixture until evenly incorporated. Taste and adjust seasoning, adding up to another 1/4 teaspoon salt or a few grinds of pepper if desired.

Bake (or serve chilled)

Preheat the oven to 375°F (190°C). Transfer the dip to a 9-inch (23 cm) ovenproof baking dish or a shallow cast-iron skillet, smoothing the top. Sprinkle the reserved mozzarella and Parmesan evenly over the top and drizzle the optional olive oil lightly.

Bake for 20–25 minutes, until the dip is bubbling around the edges and the top is golden and slightly browned. If you prefer a browner top, place under the broiler for 1–2 minutes—watch closely to avoid burning.

Remove from the oven and let rest for 5 minutes. Sprinkle with chopped fresh parsley if using, and serve warm with pita chips, toasted baguette slices, crackers, or fresh vegetable sticks. Alternatively, for a chilled version, skip baking: chill the assembled dip in the refrigerator for at least 1 hour to meld flavors, then serve cold or at room temperature.