I like to prepare the roast with a mustard coat the evening before so that the mustard can soak in a little better.
Season the Kaiser roast with pepper and paprika on all sides. Make several 2 - 3 cm deep incisions on the bottom and top of the roast. Fill the cuts with mustard and place the roast in a roasting pan. Coat the roast with the rest of the mustard.
The next day, add the onion and beer and put the tin in the oven.
Braise the roast at 175 degrees top / bottom heat for 75 - 90 minutes.