Squeeze as much liquid as possible from the thawed spinach by pressing with clean hands or squeezing in a fine-mesh sieve or cheesecloth. Measure after draining; you should have roughly 1 to 1 1/4 cups drained spinach (10 oz package yields this).

Chop the drained artichoke hearts into roughly 1/2-inch pieces so they distribute evenly through the dip.

Make the dip

Combine base ingredients

In a medium mixing bowl, beat the softened cream cheese until smooth (use a rubber spatula or electric mixer on low). Stir in the sour cream and mayonnaise until fully combined and creamy.

Add cheeses and seasonings

Fold in the shredded cheddar, shredded pepper jack, grated Parmesan, minced garlic, chopped green onions, lemon juice, kosher salt, black pepper, and red pepper flakes (if using). Mix until cheeses and seasonings are evenly incorporated.

Add vegetables

Fold the well-drained chopped spinach and chopped artichoke hearts into the cheese mixture, making sure the vegetables are evenly distributed and no large wet pockets remain.

Bake & finish

Transfer the mixture to the prepared ovenproof dish, smoothing the top with a spatula. Sprinkle the extra shredded cheddar and grated Parmesan evenly over the top.

Bake in the preheated oven for 20–25 minutes, until the dip is bubbling at the edges and the top is lightly golden. If you want a more browned top, place under the broiler for 1–2 minutes—watch closely to prevent burning.

Remove from oven and let rest for 5 minutes. Sprinkle chopped parsley or cilantro over the top if using.

Serve

Spoon the warm spinach and artichoke dip into a serving bowl or serve directly from the baking dish. Serve with fresh pico de gallo spooned alongside (or on top if preferred), tortilla chips, and warm pita wedges.

Leftovers: cool to room temperature, cover and refrigerate for up to 3 days. Reheat in a 325°F (160°C) oven until warmed through, about 15 minutes, or microwave in 30-second intervals, stirring between, until hot.