Preheat your oven to 180°C (350°F). Lightly grease your casserole dish with butter or cooking spray.

In a medium bowl, combine panko breadcrumbs, grated Parmesan cheese, melted butter, salt, and pepper. Set aside.

Melt 3 tablespoons of butter over medium heat, add minced garlic, and sauté until fragrant, about 1 minute.

Stir in ¼ cup of all-purpose flour and cook for 1 minute. Gradually whisk in 2 cups of warm milk and 1 cup of chicken broth, stirring continuously for 4-5 minutes until thickened.

Turn off the heat and stir in 1 cup of shredded cheddar cheese and ½ cup of grated Parmesan cheese until melted and combined. Season with salt and pepper to taste.

Fold in 4 cups of fresh broccoli florets until well coated with the cheese sauce.

Transfer the mixture into your prepared casserole dish and smooth out evenly. Sprinkle the breadcrumb topping over the surface.

Cover the dish with aluminum foil and bake for 25 minutes. Remove the foil and bake for an additional 20 minutes until golden brown and bubbly.

Allow it to rest for about 5 minutes before serving.