For the pasta dough:
Pre-heated oven 180FAN/200c
Place the potatoes directly onto the middle shelf of your oven and bake for 1 hour or until a knife can be inserted without resistance. Leave the potatoes to cool slightly, then slice in half and spoon out all the potato flesh (hold the potatoes with a tea towel as they’ll still be hot).
Put the potato flesh into your food processor with the blade and add a teaspoon of sea salt, the egg and a sprinkling of the flour. Pulse the machine to start incorporating the ingredients – but don’t overwork it. Soon as the potato is broken down and the egg is mostly incorporated start adding the rest of the flour in stages, pulse until it forms a dough – you may need to add slightly more or less flour. Tip the dough out of the food processor onto a lightly floured work surface and knead by hand until you have a soft pillowy dough then roll the dough into a long sausage and cut into bite size pieces and reserve.
While the dough is resting make the bechamel sauce. Melt the butter and flour in a saucepan and stir until fully combined and bubbling, you want to ‘cook out’ the flour at this stage. Remove the pan from the heat, season with salt and pepper and once it stops bubbling pour in a quarter of the milk and whisk together until smooth then pour in the rest of the milk, return to the heat and whisk continuously until it starts to bubble then remove from the heat. Stir in most of the grated cheese (saving a handful for later). You want the sauce quite loose as it will thicken while cooking with the gnocchi; aim for a thick double cream consistency.
Drop the gnocchi into the white sauce, carefully folding it together then pour into a baking dish and gently smooth the top. Using a teaspoon, dot little spots of ‘nduja around the top of the dish, gently nestling it into the sauce. Finish by scattering the remaining grated cheese on top.
Bake in the oven for 20 minutes or until it’s bubbling and finish by heating under a hot grill to brown the top. Once cooked, leave to rest for ten minutes and serve with a simple green leaf salad on the side.