Preheat oven to 400˚F (205˚C). Lightly grease a deep 10x14 inch (25x35 1/2 cm) baking dish with olive oil.
Bring a large pot of salted water to a boil. Add the penne and cook, stirring often, until just tender, al dente. Drain (do not rinse) and toss with 1 tablespoon olive oil.
In a large pan, drizzle the 1 tablespoon olive oil over medium heat. Add the onion and cook, stirring occasionally, until softened. Mix in the garlic and cook until just fragrant, 30 seconds to 1 minute. Crumble in the ground beef. Continue to cook, breaking up the beef, until browned. Season with salt and add the tomato sauce. Cook for a few more minutes until the liquid has mostly evaporated. Remove from heat and stir in the parsley.
In a large pot, melt the butter over medium heat. Stir in the flour with a whisk. Cook, while continuously stirring, just until golden. Whisk in the salt and nutmeg. Slowly pour in the milk, while continuously whisking to prevent lumps, followed by the chicken broth. Cook, stirring often to prevent the bottom from burning, until the mixture has thickened.
Remove from heat and stir in the mozzarella until smooth. In a small bowl, beat the egg. While continuously beating, pour in a little of the hot béchamel to temper the egg. Pour the egg mixture back into the pot of béchamel while whisking until smooth.
Arrange half of the cooked penne in the prepared baking dish.
Top with all of the beef mixture.
Cover the beef with the remaining penne.
Fully cover with an even layer of the béchamel sauce.
Bake the Macarona Bechamel, uncovered, in the preheated oven until golden and bubbly, 30-40 minutes.
Allow to cool for at least 15 minutes before cutting and serving.