Cook the potatoes and sweet potatoes without peeling. Leave to cool a little but remove the skins whilst warm, then put the potatoes through a food mill and into a bowl. Mix in the egg. Add the flour and salt, mix by hand. The mixture should still be moist but no longer stick to your hands. Add a little more flour if necessary. Roll the dough into sections the thickness of a finger and cut into pieces approx. 2 cm long. Place the gnocchi on a floured towel.
Cook the gnocchi in batches in gently simmering salted water for approx. 5 mins. until they float to the surface. Remove with a slotted spoon, drain.
Pumpkin seed and sage butter
Heat the butter, pumpkin seeds and sage in a wide pan until it turns frothy and tastes nutty. Toss the gnocchi in the butter and heat through.