Preheat the oven to 180°C.

Grease a 9×11 baking tray, and set it aside.

Boil the macaroni in salted water according to package directions. Once cooked, drain the macaroni and place it back into the pot, leaving it off the heat to cool down.

Melt the butter in a skillet at medium heat. Add onions, cook until softened and slightly caramelized. Scrape the onions and melted butter into the pot with the macaroni. Stir to combine.

In a large bowl, whisk the eggs until they get fluffy. Add milk, salt, pepper, garlic powder, dry mustard, dried thyme, and cayenne pepper. Stir to combine.

Pour the egg mixture over the macaroni and stir until it’s well coated.

Stir in 3 cups of the shredded cheese.

Pour everything into the greased tray and top with reserved ½ cup of shredded cheese.

Bake until the pie is firm, and the top is golden brown. About 35-40 minutes.

Allow pie to rest for 10-15 minutes before serving.