Wash the chicken, dab dry and cut the chicken in half along the breastbone with a large knife (flapping knife). (Tip: For the untrained housewife, with correspondingly missing tools, it is advisable to leave this work to the butcher). Season evenly with salt, pepper and paprika from all sides.
Brush with oil and cook in a flat roaster or baking tray in a preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: level 3) for approx. 90 minutes. Pour on half of the beer. In the meantime clean and shine the mushrooms.
Clean the leek, cut it in half lengthwise, wash it and cut it into pieces of about 5 cm. Peel onions and cut into slices. Clean, wash and quarter the tomatoes. After 30 minutes cooking time add the vegetables to the chicken.
Season with salt and pepper. 10 minutes before the end of the cooking time, pour on the remaining beer.