3 Heat up the cooking butter in a non-stick frying pan. Briefly sauté ¼ of an onion with the Wienerli sausages and the peas, and then add a ¼ of the omelette mixture. Scatter on a ¼ of the raclette cheese and allow to thicken on a medium heat, making sure that the surface remains slightly moist. Fold over once and keep warm in the oven. Repeat the process for the remaining 3 omelettes.