Had this for the first time and the flavors were bomb!

Preheat your oven to 375°F (190°C). Butter a 9×13-inch baking dish.

In a large skillet, melt the butter over medium heat. Add the onions and garlic, cooking until they are soft and translucent, about 5 minutes.

Add the cream to the skillet and bring to a simmer. Season with salt and pepper to taste.

Layer half of the potatoes in the prepared baking dish. Sprinkle half of the corn kernels over the potatoes. Pour half of the cream mixture over the corn and potatoes. Repeat with the remaining potatoes, corn, and cream mixture.

Sprinkle the cheddar cheese and Parmesan cheese evenly over the top.

Cover the dish with foil and bake in the preheated oven for 45 minutes. Remove the foil and bake for an additional 15-20 minutes, until the top is golden brown and the potatoes are tender.

Let the gratin rest for about 10 minutes before serving. Garnish with fresh parsley, if desired.