Sprinkle the remaining 1 cup of shredded mozzarella evenly over the top, making sure to cover most of the pesto swirls while still letting a little green peek through.
Place the casserole dish on the middle rack of the preheated oven and bake for 12–15 minutes, or until the cheese is melted, bubbling around the edges, and starting to turn golden brown in spots. A little pesto oil pooling on top is normal and adds flavor.
If you’d like a deeper golden top, switch the oven to broil for 1–2 extra minutes, watching closely so it doesn’t burn.
Remove from the oven and let the pesto cheese bake rest for 5 minutes before serving. This helps it set slightly so it’s extra gooey but not runny. Serve warm, scooping out big spoonfuls straight from the dish.
