Step 1: Preheat and Prepare

Preheat your oven to 375°F (190°C). Grease a 9×13-inch baking dish with olive oil to prevent sticking.

Step 2: Cook the Broccoli

If using fresh broccoli, steam it until tender (about 5 minutes). For frozen broccoli, microwave for 3-4 minutes until thawed and tender. Set the cooked broccoli aside.

Step 3: Make the Cheddar Cheese Sauce

In a medium-sized saucepan, melt the butter over medium heat. Whisk in the flour to create a roux, cooking for 1-2 minutes until lightly golden. Gradually pour in the milk and heavy cream, whisking continuously to prevent lumps. Once the mixture thickens (about 3-4 minutes), stir in the garlic powder, onion powder, and paprika. Remove from heat and mix in the shredded cheddar cheese until melted and smooth. Season the sauce with salt and pepper.

Step 4: Layer the Potatoes and Broccoli

Layer half of the sliced potatoes in the prepared baking dish. Top with half of the cooked broccoli florets. Pour half of the cheese sauce over the layer. Repeat with the remaining potatoes, broccoli, and cheese sauce.

Step 5: Bake the Dish

Cover the dish with aluminum foil and bake in the preheated oven for 45 minutes. The potatoes should be fork-tender.

Step 6: Add Crispy Onion Topping

Remove the foil and sprinkle the crispy fried onions and grated Parmesan cheese over the top. Return the dish to the oven and bake for an additional 15-20 minutes, or until the top is golden brown and crispy.

Step 7: Let It Rest

Once baked, let the dish rest for about 10 minutes before serving. This will help the layers set and make it easier to slice and serve.