Step 1: Prepare the Potatoes

1. Preheat your oven to 375°F (190°C).
2. Peel and dice the potatoes into ½-inch cubes or shred them using a box grater or food processor. Place the diced potatoes in a large pot of salted water and bring to a boil.
3. Cook the potatoes for 8-10 minutes, or until just tender but not falling apart. If using shredded potatoes, skip this step and proceed directly to assembling the dish.
4. Drain the potatoes and set them aside to cool slightly while you prepare the cream sauce.

Step 2: Make the Cream Sauce

1. In a medium saucepan, melt 3 tablespoons of butter over medium heat. Once melted, add the flour and whisk continuously for 1-2 minutes to create a roux.
2. Gradually pour in the milk and heavy cream, whisking constantly to prevent lumps.
3. Add garlic powder, onion powder, thyme, paprika (if using), salt, and pepper. Continue whisking until the sauce thickens, about 3-5 minutes.
4. Remove the sauce from heat and stir in ½ cup of cheddar cheese and ¼ cup of Parmesan cheese. Whisk until the cheese is fully melted and the sauce is smooth.

Step 3: Assemble the Dish

1. Grease a 9×13-inch baking dish with 2 tablespoons of butter.
2. Layer the cooked (or raw shredded) potatoes evenly in the prepared dish. Pour the cheese sauce over the potatoes, ensuring every piece is coated. Gently stir to combine if needed.
3. Sprinkle the remaining 1 cup of cheddar cheese and ¼ cup of Parmesan cheese over the top. If desired, add a layer of breadcrumbs for extra crunch.

Step 4: Bake

1. Place the baking dish in the preheated oven and bake for 30-35 minutes, or until the top is golden brown and bubbly.
2. If the topping isn’t golden enough, broil for 2-3 minutes, keeping a close eye to prevent burning.

Step 5: Serve

1. Remove the dish from the oven and let it rest for 5 minutes before serving.
2. Garnish with chopped parsley (if desired) and serve warm.