Preheat and Prep: Preheat your oven to 180°C (160°C fan). Lightly grease a 23x33cm (9x13 inch) baking dish.

Cook the Pasta Shells: Bring a large pot of salted water to a boil. Add the pasta shells and cook according to package directions, but for 2 minutes less than the minimum time so they are slightly undercooked (al dente). This prevents them from becoming mushy in the oven. Drain carefully and rinse with cold water to stop the cooking process.

Make the Chicken Alfredo Filling: In a large bowl, combine the shredded chicken, softened cream cheese, 100g of grated Parmesan, the grated mozzarella, chopped parsley, and dried oregano. Season well with salt and black pepper. Mix until everything is thoroughly combined.

Stuff the Shells: Carefully spoon the chicken mixture into each cooked pasta shell. I find that using a piping bag or a simple zip-top bag with the corner snipped off makes this step much quicker and less messy. Arrange the stuffed shells snugly in your prepared baking dish.

Create the Garlic Butter Sauce: In a medium saucepan, melt the unsalted butter over a medium heat. Add the minced garlic and cook for about 1-2 minutes until fragrant, being careful not to let it brown.

Finish the Sauce: Pour in the double cream and chicken stock. Whisk to combine and bring to a gentle simmer. Let it bubble gently for 3-4 minutes, stirring occasionally, until it has thickened slightly. Season with a pinch of nutmeg, salt, and pepper. For a truly velvety sauce, it's important not to let it boil rapidly, as explained in this guide to making stable cream sauces.

Assemble and Bake: Pour the finished garlic butter sauce evenly over the stuffed shells in the baking dish. Sprinkle with a little extra grated Parmesan.

Bake to Perfection: Place the dish in the preheated oven and bake for 20-25 minutes, or until the sauce is bubbling and the cheese on top is melted and lightly golden. Let it rest for 5 minutes before serving to allow the sauce to settle.