Preheat oven to 350 degrees. Spray a 9x13 inch pan with cooking spray and set aside.
In a medium saucepan add butter, heavy whipping cream, and cream cheese. Cook over medium heat and whisk until melted. Add the minced garlic, garlic powder, italian seasoning, salt and pepper. Continue to whisk until smooth. Add the grated parmesan cheese. Bring to a simmer and continue to cook for about 3-5 minutes or until it starts to thicken. Remove from heat.
Pour 1 cup of the homemade alfredo into the bottom of your 9x13 inch pan.
Cook the jumbo shells according to package directions. Drain and rinse in cold water. In a medium sized bowl add the shredded chicken, 2 cups mozzarella cheese, broccoli, and 1 1/2 cups homemade alfredo. Stir and stuff each shell with mixture. Place in prepared 9x13 inch pan.
Pour remaining alfredo on top of the shells and top with 1/2 cup mozzarella cheese. Bake for 25-30 minutes or until heated through and bubbly.
Top with freshly grated parmesan cheese if desired.