Spread the sunflower seeds out on a baking tray so you have one layer. Roast in the oven until they are lightly brown. Don't let them become too dark or it will be bitter. And it goes quickly so stay close to the oven.
Let it cool a bit before transferring to your food processor. Blend the seeds together. It will first become like sand, than wet sand and after a while longer it will all clump together and sort of stay fixed in your food processor. That is normal. Keep breaking up the clump in between and repeat the process until - at some point - it will let go and transform into a smooth butter.