First, preheat your oven to 180°C (160°C fan) and lightly grease a 2-litre ovenproof casserole dish.

In a large, heavy-based pan or sauté pan, melt the butter over a medium heat. Add the chopped shallots and cook gently for 3-4 minutes until they have softened and become translucent, but not browned.

Stir in the minced garlic and cook for another minute until you can smell its wonderful aroma. Be careful not to let it burn.

Sprinkle over the plain flour and stir continuously for 1-2 minutes. This cooks out the raw flour taste and creates a 'roux', which will thicken our sauce.

Gradually pour in the white wine, whisking as you go to prevent lumps. Let it bubble away for a minute to cook off the alcohol and reduce slightly.

Slowly add the stock, followed by the double cream, whisking constantly until the sauce is completely smooth. Bring the mixture to a gentle simmer and let it cook for 3-5 minutes, stirring occasionally, until it has thickened enough to coat the back of a spoon.

Remove the pan from the heat. Stir in the Dijon mustard, the zest and juice of the lemon, most of the chopped parsley, and half of the grated Parmesan. What works best for me is tasting the sauce at this stage and seasoning generously with salt and black pepper. It should be rich and full of flavour.

Gently fold the dry, raw prawns into the creamy sauce, ensuring they are all evenly coated. Pour this mixture into your prepared casserole dish and spread it out evenly.

In a small separate bowl, combine the grated Gruyère, the remaining Parmesan, and the panko breadcrumbs. Sprinkle this mixture evenly over the surface of the casserole.

Bake in the preheated oven for 15-20 minutes. You'll know it's ready when the sauce is gently bubbling at the edges and the topping is crisp and a beautiful golden brown.

Allow the casserole to rest for 5 minutes before serving. This lets the sauce settle slightly. Garnish with a final sprinkle of fresh parsley and serve hot.