Slice the onions thinly and heat olive oil in a large skillet over medium heat. Add the onions and cook for 30–40 minutes, stirring occasionally, until they turn golden brown and caramelized. If the onions start to stick, add a splash of beef broth to deglaze the skillet.

In the same skillet once the onions are done, melt the butter over medium heat. Whisk in the flour until smooth, then slowly add the heavy cream, stirring until thickened, about 5–7 minutes. Fold in the caramelized onions, season with salt and pepper, and mix in the Parmesan until creamy.

Bring a large pot of salted water to a boil and add the cavatappi macaroni. Cook until al dente, about 1–2 minutes shy of package instructions. Drain and reserve a cup of pasta water.

Preheat the oven to 350°F (175°C). In a bowl, mix the cooked pasta with the béchamel sauce until well combined. Transfer to an oven-safe baking dish, spreading the remaining caramelized onions on top and sprinkle with breadcrumbs.

Bake for 10–15 minutes, or until the top is golden brown and bubbly.

Let the dish cool for a couple of minutes, garnish with parsley, and serve.