In a large skillet, heat a tablespoon of oil over medium heat. Add thinly sliced onions and sauté for 30 to 40 minutes, stirring occasionally, until golden brown and caramelized.

Once the onions are caramelized, push them to the side of the skillet. Melt 2 tablespoons of butter in the cleared space, then whisk in 2 tablespoons of flour. Cook for about 1-2 minutes until bubbly.

Gradually pour in 1 cup of heavy cream, whisking constantly until the sauce thickens. Stir in ⅔ of the caramelized onions, salt, pepper, and parsley.

In a large pot, bring salted water to a boil and add the cavatappi macaroni. Cook until just under al dente, about 1-2 minutes shorter than package instructions. Drain the pasta, reserving a cup of cooking water.

Add the drained pasta to the béchamel sauce in the skillet, mixing until well combined. Transfer to a baking dish, top with remaining caramelized onions and breadcrumbs.

Preheat your oven to 350°F (175°C), then bake uncovered for 10 to 15 minutes until the top is golden brown.

Remove from the oven, allow to cool slightly, garnish with fresh parsley, and serve hot.