Add the gnocchi to a large pan of salted water and cook for 2-3 minutes.
Start making the sauce by adding the butter to a medium pan on a medium heat. When its melted add the flour, mustard powder and cayenne pepper and stir together till well combined. Turn the heat right down and start adding the milk slowing, stirring as you go constantly. Once all the milk in added, stir through the grated cheeses a part from the parmesan, until the sauce starts to thicken. Season to taste.
Stir through the gnocchi and lardons and transfer to a suitable sized ovenproof dish. Sprinkle over the parmesan, dollop over the ricotta and distribute the herb leaves. Place in the oven for around 15 minutes until the parmesan has melted, the sauce is bubbling and the leaves have crisped.