Cook the pumpkin in a pressure cooker for 2 minutes until soft.
Cook the potatoes in salted water until soft, then peel and press through a ricer onto a floured surface. Mix with the pumpkin and leave to cool. Mix the egg, egg yolk and salt into the potato-pumpkin mixture and knead with enough flour to form a loose, homogeneous dough. Keep your hands floured so the dough does not stick to them.
Divide the dough into small portions and from each portion form finger-thick rolls with your floured palms. Cut the rolls into 2-3 cm pieces (approximately 1 inch) and flatten with a fork. Dust each piece lightly with flour.
Bring salted water to a boil in a large pot. Slide the gnocchi into the water in small quantities and cook covered for 3-5 minutes over low heat. The gnocchi are done when the rise to the surface. Remove them with a slotted spoon and drain well, then place onto 4 plates. Melt the butter over low heat and pour over the gnocchi. Rinse the arugula and spin dry. Serve the gnocchi with the arugula, garnished with parmesan and pepper.