Grind the wheat only briefly (whole grains should be partially preserved). Leave to swell in 300 ml water at low heat for about 25 minutes. Mix with the rye and wheat meal.
Add the sourdough, crumbled yeast, salt, sugar and 1/2 litre lukewarm water. Knead everything with the dough hooks of the hand mixer to a bubbly dough. Cover and leave to rise for 30 minutes. Dice plums roughly.
Knead together with the hazelnuts under the dough (rather liquid consistency). Pour into a greased box form and leave to rise for another 15 minutes. Then bake in a preheated oven (electric cooker: 200 °C/ gas: level 3) for about 1 1/2 hours.
In addition, place a water-filled, ovenproof container in the oven. Results in about 25 slices.