Preheat your oven to 400°F.

Set a large skillet over medium-high heat, melt 4 tablespoons of butter, and cook the onions until softened, about 2 minutes. Add the garlic, salt, and black pepper, and cook for an additional 30 seconds.

Add the chopped kale to the skillet in batches, allowing it to wilt before adding more. Continue until all the kale is incorporated and softened.

Reduce medium heat, then stir in the heavy cream, cream cheese, and Parmesan. Continue stirring until the cheeses are melted and the mixture is smooth.

Transfer the kale mixture to an 8x8-inch baking dish.

In a small bowl, mix the Panko breadcrumbs with the chopped parsley and melted butter. Sprinkle this mixture evenly over the kale.

Place the casserole in the oven and bake for 10 minutes, until the topping is golden brown. Serve hot.