Preheat your oven to 350 degrees F and adjust the rack to the top third of the oven. Grease a 9x13-inch baking dish lightly with olive oil and set aside.

In a medium bowl, stir together the breadcrumbs and 4 tablespoons of olive oil. Add a pinch of kosher salt and freshly ground black pepper, then set aside for topping.

Place the chicken breasts in a large pot and cover them with water. Add 4 teaspoons of salt, bring the water to a boil, then reduce to a gentle simmer. Poach the chicken for 15-20 minutes or until an instant-read thermometer registers 160 degrees F internally.

Let the chicken cool slightly before slicing it thinly or shredding it completely. Arrange the cooked chicken evenly in the bottom of the prepared baking dish.

Blanch the broccoli florets by boiling them in salted water for 3-4 minutes until bright green and slightly tender. Drain and immediately transfer them to an ice bath to preserve their color. Spread the broccoli evenly over the chicken.

Sprinkle the grated Parmesan cheese over the broccoli and chicken, ensuring full coverage.

In a medium saucepan, melt the butter over medium heat. Once melted, whisk in the flour and cook for 4-5 minutes to eliminate any raw flour taste. Stir in the cayenne and nutmeg for seasoning.

Gradually whisk in the milk, followed by the shredded cheddar and chicken stock. Continue whisking to create a smooth and thickened sauce, about 5-8 minutes. Pour the sauce evenly over the chicken and broccoli layers.

Top the casserole with the breadcrumb mixture, ensuring it’s evenly distributed, then sprinkle the paprika over the top for color.

Cover the dish with foil and bake for 15 minutes. Remove the foil and bake for an additional 15 minutes, or until the casserole is bubbling and the topping is golden brown.

Let the casserole cool for 5 minutes before serving. Enjoy!