Add 2 cups of oats to a food processor, blitz until you get a fine powder, remove the oat flour to a large mixing bowl.
Add 1 cup of oats to the food processor, pulse a few times until most of the oats have been broken down a little, like the look of quick oats, add to the mixing bowl.
Add the remaining 2 cups of oats into the mixing bowl along with the cinnamon, salt and chopped nuts.
To a small saucepan add the butter, brown sugar, sugar and water, bring to a boil for 1 minute, remove from the heat and stir in the vanilla extract.
Pour the hot sugar mixture over the oats and stir till thoroughly combined, then add the egg whites and stir again.
Scrape the mixture onto a large rimmed baking sheet and spread evenly across the sheet.
Bake at 300F for 45 minutes or until dark golden brown in color and mostly dry to the touch.
When you remove the granola from the oven take a large spatula and loosen it from the pan but DO NOT stir it or rassel it around. Once complexly cooled break the larger chunks up into smaller bite sized pieces and store in a zip top bag.