Put the oil in a pan and let it get hot. Fry the meat cubes in it, season with salt, pepper and place in the slow cooker. Briefly roast the onions, carrots and celery and add to the meat. Pour the malt beer and the stock into the pot, boil off the sediment and then pour over the meat and onions. Stir in paprika powder, caraway seeds, mustard and tomato paste. Put the lid on and cook everything for 6.5 hours on the LOW setting.
Dissolve the cornstarch in a cup of cold water and stir into the saucepan. Set to HIGH for another 30 minutes until the sauce thickens.