Start by rinsing the shrimp and scallops under cold water, then pat them dry with paper towels.

In a large skillet, melt 2 tablespoons of butter over medium heat. Add the chopped onion and minced garlic, sautéing for 3-4 minutes until translucent.

Add the prepared shrimp and scallops to the skillet, cooking for about 3 minutes until shrimp turns pink and scallops become opaque.

Pour in ½ cup of white grape juice into the skillet, stirring to combine. Allow it to simmer gently for 2 minutes.

Stir in 1 cup of heavy cream, along with salt and pepper to taste. Mix everything thoroughly until well combined.

Transfer the seafood mixture into a greased baking dish, and sprinkle 1 cup of grated cheese on top.

Preheat your oven to 180°C (350°F) and bake for 15 minutes or until the cheese is bubbly and golden brown.

Once baked, let the Seafood Gratin cool slightly for about 5 minutes before serving.