Preheat the oven to 180°C and line a baking sheet with parchment paper.
Grind the oats in a small blender or food processor.
Add the cashew butter, the peanut butter, the sugar and the egg to a large bowl and stir with a spoon until combined.
Add the ground oats, the cornstarch and the baking soda to the bowl and combine the ingredients with your hands.Note: it is important to get them slightly greasy to form the cookies more easily afterwards.
Roll the dough gently into small balls and place them on the baking sheet. Then, press down with a fork twice.
Bake for 15 minutes at 180°C.
Remove from the oven and sprinkle a little sea salt. Let cool on the baking sheet for at least 30 minutes.