This fast food take on Kenji's Hasselback potato gratin layers McDonald's hashbrowns in a rich, cheesy sauce--a combination of heavy cream with Gruyère and Parmesan, seasoned with raw garlic, thyme, and a hefty dose of black pepper. It's the perfect bath for the already-fatty potatoes to soak in as their tops crisp up in the oven.
- 4 ounces finely grated Gruyère cheese
- 2 ounces finely grated Parmesan cheese
- 1 1/3 cups heavy cream
- 3 cloves garlic, minced or grated on a microplane
- 1 teaspoon fresh thyme leaves, minced
- Kosher salt and freshly ground black pepper
- 10 McDonald's hash browns, cut crosswise into thirds
- 1 tablespoon butter
- 1 cup canned fried onions fried shallots
Adjust oven rack to middle position and preheat oven to 400°F. Combine Gruyère and Parmesan in a large bowl with cream, garlic, and thyme, season with salt and lots of black pepper.
Grease a 2-quart baking dish with butter. Pour the cream mixture into the baking dish in an even layer, being sure not to get excess mixture on the sides of the dish. Place the cut hash browns into the mixture in three rows, ensuring the tops of the hash browns remain above the liquid, partially submerged. Bake, rotating once during cooking, until liquid is bubbling and edges are starting to brown, 20 minutes. Top with fried onions and return to oven for 10 minutes. Remove from oven, let rest 5 minutes, and serve.