Preheat your oven to 375°F (190°C). Thoroughly wring out the thawed spinach in a clean kitchen towel to remove all water. Drain and roughly chop the artichoke hearts.

In a large bowl, use a mixer to beat the softened cream cheese, sour cream, and mayonnaise until smooth and fluffy. Add the minced garlic, salt, and black pepper, mixing until combined.

Using a spatula, gently fold the dry spinach and chopped artichokes into the cream cheese mixture. Stir in half of the mozzarella and half of the Parmesan cheese.

Transfer the mixture into a rustic 1-quart ceramic bowl and smooth the top. Sprinkle the remaining mozzarella and Parmesan cheese evenly over the surface. Bake for 20-25 minutes until the edges are bubbling.

Turn the oven to broil for the final 1-2 minutes, watching closely, until the cheese forms a perfectly golden-brown bubbly crust.

Brush baguette slices with olive oil and toast in the oven until crisp. Serve the warm dip alongside the toasted crostini.