Grease an ovenproof dish (approx. 18 x 25 cm) with a little oil and pour the remaining oil into the dish. Place the mould in the oven and preheat it (electric cooker: 250 °C/ circulating air: 225 °C/ gas: level 5). Peel onions and cut into slices. Wash apples, dab dry, quarter and core them. Wash and drain sage
Put the sausages, onions and apples into the hot pan and bake for 15-20 minutes. If necessary turn once in a while
Mix flour, salt, mustard powder and possibly some pepper. Whisk the eggs, mix with milk and flour to a smooth dough. When the sausages start to brown, reduce the oven temperature (electric cooker: 225 °C/ circulating air: 200 °C/ gas: level 4). Remove the mould from the oven. Spread sage leaves over the contents and pour the dough evenly over it. Put back into the oven and bake for another 20-25 minutes