Mix flour and water and let it autolyze for 60 minutes. Add salt and sourdough starter and mix it thoroughly into the dough.

Place the seeds in a heatproof container and cover with boiling water. Let it cool. Or, toast the seeds in a skillet on medium heat until the start to get some color, about 1,5-2 minutes. Start with the pumpkin and sunflower seeds and add the linseed the last 30 seconds.

Perform 4-5 stretch and folds during bulk fermentation. Perform the first 15 minutes after you have added salt and starter, and space out the rest with 15-30 minutes intervals. You may have to increase or decrease the amount of stretch and folds depending on how the dough behaves. If you feel a lot of resistance, it's time to stop. You can also check the dough with the windowpane test. Add the seeds when you perform the first stretch and fold.

Total time for bulk fermentation should be about 4-6 hours, depending on temperature, the strength of starter, etc. When the dough has increased about 50-70% in volume it is ready.

Tost the oats in a skillet slightly. Ground it in a pestle and mortar.

Dump out the dough on your working surface and shape it into a round with your bench knife. Let the dough rest for 15-30 minutes, giving it time to relax a bit. Shape the dough into your preferred shape.

Flour a banneton and sprinkle with the toasted oats. Place the loaf in the banneton and let it proof for 1- 1,5 hours at room temperature. You can also let it proof longer, 8-14 hours, in your refrigerator, depending on temperature. Make finger poke tests regularly to make sure the dough is not over-proofed.

Preheat the oven to 480ºF/250ºC. Score the loaf and bake it for 45-50 minutes. If you are using a dutch oven or a clay cooker, remove the lid after 15 minutes. You may have to reduce the heat in the last 15-20 minutes.

Let the loaf cool on wire racks.