Pesto Spinach Mac and Cheese

Preheat the oven to its highest temperature setting, which is 350 degrees Fahrenheit. Next, take a casserole dish and apply a thin layer of cooking oil to prevent food from sticking.

Bring a large container of salted water to its boiling point. Then, cook elbow macaroni in the boiling water, stirring occasionally until it reaches a tender yet still slightly firm texture, approximately 8 minutes. During the last minute of cooking, add a handful of baby spinach leaves to the pot; drain the water afterwards.

In a saucepan, melt 2 tablespoons of butter over medium heat. Add sliced onions to the saucepan and cook until they become translucent, about 3 minutes. Stir minced garlic into the onion mixture and continue cooking for another minute until fragrant. Whisk together 2 tablespoons of pesto, flour, black pepper, and salt until you get a smooth mixture. Gradually add milk to the onion mixture and continue cooking until it thickens slightly, about 2 minutes. Stir in 1 1/2 cups of Cheddar cheese, 1/2 cup of Parmesan cheese, and 1/2 cup of Asiago cheese until the cheese is fully melted. Remove the saucepan from heat.

Combine the cooked macaroni with the cheese mixture, stirring until well combined. Pour the macaroni mixture into a prepared casserole dish and cover it with aluminum foil.

Place the casserole dish in a preheated oven at 350 degrees Fahrenheit for 25 minutes. Remove the casserole dish from the oven, increase the oven temperature to its highest setting of 450 degrees Fahrenheit. Melt the remaining 1 tablespoon of butter in a small saucepan and stir it with the remaining 2 tablespoons of pesto, 1/4 cup of Cheddar cheese, 1/4 cup of Parmesan cheese, and 1/4 cup of Asiago cheese along with some bread cubes. Remove the casserole dish from the oven, uncover it, and top it with the bread mixture.

Bake the casserole dish in the preheated oven, uncovered, until it is golden brown and bubbly, approximately 10 minutes.