01 - Preheat oven to 400°F (200°C). Line a baking sheet with parchment paper.
02 - Pierce russet potatoes several times with a fork. Place directly on oven rack and bake for 45 to 50 minutes, until tender. Allow to cool slightly.
03 - While potatoes bake, steam broccoli florets in a steamer or saucepan for 3 to 4 minutes, until bright green and just tender. Set aside.
04 - Slice baked potatoes in half lengthwise. Using a spoon, gently scoop out most of the flesh, leaving a 1/4-inch shell. Reserve potato flesh for another use.
05 - Brush cut sides and exteriors of potato skins with melted butter using a pastry brush. Arrange cut-side up on baking sheet and sprinkle with garlic powder, salt, and black pepper.
06 - Bake seasoned potato skins for 10 minutes. Flip and bake an additional 5 minutes, until edges are golden and crisp.
07 - In a mixing bowl, combine steamed broccoli, Alfredo sauce, half the shredded mozzarella, and half the grated Parmesan. Mix thoroughly.
08 - Spoon broccoli-Alfredo mixture into each potato shell, mounding slightly. Sprinkle with remaining mozzarella and Parmesan.
09 - Return filled potato skins to the oven and bake for 10 to 12 minutes, until cheese is melted and bubbling.
10 - Remove from oven and garnish with chopped parsley if desired. Serve hot.