Step 1: Preheat your oven to 375°F (190°C). Lightly grease a 9x13 inch baking dish.
Step 2: Dice the potatoes into 1-inch pieces. Place them in a pot of salted water and bring to a boil. Cook for 5-7 minutes, or until just tender-crisp. Drain well.
Step 3: While potatoes are cooking, blanch the broccoli florets by boiling them in water for 2-3 minutes, then immediately plunging them into ice water to stop cooking. Drain and chop if necessary.
Step 4: In a large bowl, whisk together the cream of chicken soup, milk, sour cream, onion powder, garlic powder, salt, and black pepper until smooth.
Step 5: Add the drained potatoes, cooked chicken, and blanched broccoli to the soup mixture. Stir gently to combine, ensuring all ingredients are well coated.
Step 6: Spread half of the mixture evenly into the prepared baking dish. Sprinkle with 1 cup of shredded cheddar cheese.
Step 7: Top with the remaining chicken and potato mixture. Sprinkle the remaining 1 cup of cheddar cheese over the top.
Step 8: Bake for 25-30 minutes, or until the casserole is bubbly and the cheese is melted and golden brown. Let stand for 5 minutes before serving.