Crumble 30 g yeast in 300 ml lukewarm water and dissolve while stirring. Stir in 150 g each of spelt flour and wholemeal spelt flour, cover with foil and leave to rise overnight at room temperature.
The next day, crumble the remaining yeast (12 g) into 300 ml lukewarm water and dissolve while stirring. Mix 300 g flour and wholemeal flour and 2 tsp. salt in a large bowl. Add yeast water and dough from the previous day to the flour. Knead everything with the dough hooks of the mixer to a smooth dough. Cover with a tea towel and leave to rise in a warm place for about 2 hours.
Coat a box mould (30 cm long) with oil and dust with flour. Knead the dough on a floured work surface again briefly. Shape into an oblong loaf, place in the box mould, cover and leave to rise in a warm place for approx. 30 minutes.
Preheat oven (electric cooker: 200 °C/circulating air: 180 °C/gas: see manufacturer). Score the surface of the dough with a sharp knife several times at an angle. Bake in a hot oven for about 45 minutes. Remove bread from the oven, turn out onto a cake rack and let it cool down.