For the red cabbage bun, first toast the sunflower seeds in a coated pan until golden brown, then let cool. Clean the red cabbage, cut into strips about 4 mm thick and knead vigorously by hand in a bowl together with 3 g salt so that juice comes out. Then knead in the sunflower seeds and let everything sit for 30 minutes.
Put the wheat flour in the dough mixer with the whole spelt flour, sourdough, yeast, remaining salt and water, mix in slow speed for 4 minutes and knead in faster speed for 6 minutes. Once the dough is smooth and kneaded out (“window test”), add the red cabbage and knead in slow speed for about 1 minute. Brush a bowl with oil, place the dough in it, cover with baker’s twine and let it rest at room temperature for 45 minutes. Fold the dough once in the bowl, cover with plastic wrap and let it mature in the refrigerator for about 15 hours.
On baking day, remove the dough from the refrigerator and let it come to room temperature for 30 minutes. Preheat the oven to 260 °C convection with the baking stone inserted (lower third). Carefully transfer the dough to the floured work surface and lightly flour the top as well. Gently shape into an oblong shape and divide lengthwise into two equal-sized strands. Roll up each strand with the floured side facing inward, place on a baking sheet with parchment paper with the snail pattern facing up, and sprinkle with a little flour. Cover with baker’s twine