Mix the different types of flour and 1 tablespoon of salt in a bowl. Heat 450 ml of water lukewarm, add yeast and dissolve in it. Add sourdough, mix everything and add the liquid with 75 g sunflower seeds to the flour. Knead everything briefly with the dough hooks of the hand mixer.
Dust the work surface with flour. Place the dough on the work surface and knead with your hands until the dough is smooth. Place the dough in the bowl, dust with some flour, cover with a tea towel and leave to rise in a warm place for 30-45 minutes until the dough has increased in size. Knead dough again and form into a ball.
Line baking tray with baking paper. Place bread dough on top and cut into it with a sharp knife about 1 cm deep. Dissolve 1 teaspoon of salt with 2 teaspoons of hot water and coat the rye bread with it. Sprinkle the remaining sunflower seeds over it and press it on. Let the bread dough rise for another 15-20 minutes. Bake in the preheated oven (electric cooker: 225 °C/gas: level 4) for about 15 minutes. Turn down the temperature (electric oven: 200 °C/gas: level 3) and continue baking for 30-40 minutes. Tap the loaf of bread from below. If it sounds hollow, the bread is cooked through.