Peel the potato, cut into chunks and cook in boiling water until tender; drain well. Using a potato masher, mash the potato with the butter.
Sift the flour, ½ tsp of salt and the baking powder into a bowl. While the mash is still warm, stir into the flour and combine well with the cheese and spinach. Using lightly floured hands, gently shape this mixture into two balls and turn onto a l