Preheat the oven to 150ºC. Divide the sunflower seeds over a baking tray and roast them in the oven for 10-15 minutes.
Kneading by machine
Put the flour, water, sourdough, yeast and salt in the mixing bowl. Mix everything at low speed for 5 minutes and then at high speed for 10 minutes. Add the olive oil 3 minutes before the end and at last the seeds at low speed.
Pour the flour onto the worktop and make a hole in the middle. Put half of the water, sourdough and yeast and the salt in it.Mix everything by hand and then add the rest of the water, the olive oil and the seeds. Knead the dough until it is smooth and supple.
Form a ball from the dough and cover it with a damp tea towel. Let rise for 2 hours. Fold the dough half way through the rising time.
Spray the worktop with flour. Divide the dough into 4 equal pieces. Roll the pieces of dough over the worktop until they are elongated. Cover them with a tea towel and let rest for 15 minutes.
Carefully press the pieces of dough flat with your palm. Take a piece of dough, fold over a third and press it with your fingertips. Fold over the remaining piece and press it with your fingers.
Sprinkle the leftover kernels on the worktop. Place the pieces of dough with the seam downwards and fry the top with a brush of water. Place the pieces of dough with the moist side on the pits so that they stick to it.
Place the pieces of dough with the seam down on a baking sheet with parchment paper and let rise for another hour, covered with a damp tea towel.
Preheat the oven to 235 ºC and pour just before you put the loaves in the oven water on the hot griddle.
Put the ciabattas in the oven and bake at 235ºC for 4 minutes. Lower the temperature to 220 ° C and bake for another 11 minutes.
Brush the top of the ciabattas with olive oil and let cool on a rack.