Prick the potatoes all over with a fork and put on a large baking sheet. Bake in a preheated oven, 220°C (425°F), Gas Mark 7, for 1 hour, or until cooked through – to test, pierce the largest potato with a blunt knife.
When cool enough to handle, halve the potatoes and scoop the flesh out into a bowl. Mash in the Parmesan, rocket, lemon rind and half the butter. Add the nutmeg and season with salt and pepper.
Roll the pasta dough out into long sheets (see
Cook the pasta in a large saucepan of salted boiling water for 2–3 minutes until al dente. Drain, reserving a ladleful of the cooking water.
Meanwhile, melt the remaining butter in a large frying pan over a low heat. Add the ravioli and its reserved cooking water and simmer gently until coated in a silky sauce. Serve immediately with a scattering of Parmesan shavings and rocket.