Mix the cornflour, flour, oil, water and salt with an electric mixer until smooth. Then knead the dough well. Peel and dice the onion, and fry in hot oil. Add the spinach and sour cream. Season with salt, pepper and nutmeg. Divide the dough into 12 pieces, roll each piece out thinly with a pasta machine or on a floured work surface. Place about 1 tsp. of filling in the centre of the dough. Brush the edges of the dough with water and fold the rest of the dough over it, pressing it down well. Cook the ravioli in salted water for approx. 10 min.