Preheat oven to 375 degrees F (190 degrees C).
Add Wild Rice (2 cup) to a medium pan with Chicken Broth (3 cup). Bring to boil then reduce to low and cover the pan. Cook until rice just breaks open and slightly tender about 35 minutes. Set aside.
Cut the Broccoli (3 head) into florets. Bring a pot of water to a boil. Blanch the broccoli by throwing the florets into the boiling water until bright green and still crisp, 1 to 2 minutes.
Immediately drain broccoli and plunge it into bowl of ice water to stop the cooking.
Remove from ice and set aside.
In large pot over medium heat, melt Butter (1/2 cup). Add the finely chopped Button Mushroom (1 pound), finely diced Onion (1) and cook 3 to 4 minutes.
Add finely diced Carrot (2) and finely diced Celery (2 stalk) and cook until soft.
Sprinkle the All-Purpose Flour (1/4 cup)on the veggies and stir to mix. Pour 3 more cups of Chicken Broth (3 cup) over that and combine with Heavy Cream (1/2 cup). Bring to gentle boil and allow to thicken. Add Salt (1 teaspoon) and Ground Black Pepper (1 teaspoon).
Mix together the rice and broccoli and place in a 3-quart baking dish. Next, scoop out veggie mixture and spoon it evenly over the top of rice.
Melt remaining butter and mix withPanko Breadcrumbs (1 cup). Sprinkle this mixture over the top of casserole.
Cover with foil and bake for 20 minutes at 375 degrees F (190 degrees C).
Remove foil and bake 15 minutes more.
Garnish with Fresh Parsley (2 tablespoon), if desired after out of oven. Enjoy!