Rinse the shrimp and scallops under cold water. Peel the shrimp and chop the scallops into bite-sized pieces for even cooking. Set aside.

In a skillet over medium heat, melt a tablespoon of butter. Add the chopped onion and minced garlic, sautéing for about 3-4 minutes until the onion is translucent and fragrant.

Toss the shrimp and scallops into the skillet. Cook for approximately 3 minutes until the shrimp turns pink and the scallops are opaque.

Pour in the white grape juice, letting it simmer for 2 minutes to reduce slightly. Stir in the heavy cream, salt, and pepper until everything is well combined and creamy.

Transfer the seafood mixture into a baking dish, spreading it out evenly. Sprinkle your chosen grated cheese generously over the top.

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

Allow the gratin to cool for a couple of minutes before serving.