Mix 2 teaspoons of salt, pepper and paprika powder. Wash the meat, dab dry and season all around. Coat with mustard. Pour onto the oiled fat pan and cook in the preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: level 3) for about 2 1/2 hours.
Cover the roast after 1 1/2 hours with aluminium foil. For the polenta, boil milk and 750 ml water. Add 1 tablespoon butter and about 1 teaspoon salt. Stir in semolina. Continue stirring over low heat for 5 minutes.
Finish cooking for a further 15 minutes on a switched-off hotplate. Season to taste with mace. In the meantime, wash and clean the beans and cut them into small pieces depending on their length. Cook in boiling salted water for about 15 minutes.
Peel and chop the onion. Heat the remaining butter and sauté the onion until transparent. Drain the beans, add to the onions and sauté briefly. Season to taste with salt and pepper. Cut the meat into slices and arrange on a plate with the beans.
Dissolve the roast with 4 tablespoons of water. Arrange polenta, beans, meat and roast on plates.