In a large bowl, or a bowl of a stand mixer, cream together the softened butter and sugars on medium speed until light and fluffy. 4-5 minutes.
225 g unsalted butter,, 100 g granulated white sugar, 200 g brown sugar
Scrape down the sides of the bowl, then on a lower speed add in the eggs and yolk, one at a time, until well mixed in, add in the vanilla extract and mix again.
In a separate bowl, weigh out the flour, sifting if needed, and then add the oats, baking soda, salt and spices.
Add the flour mixture to the butter mixer and mix on low, scraping the sides and bottom of the bowl when necessary, to ensure all the flour is mixed in.
Add in all of the mix-ins and carefully mix until all is combined. You can use a spatula for this step.
Chill the dough a minimum of 2 hours up to overnight in a bowl covered with plastic wrap pressed agains the dough and another piece over the rim of the bowl.
When ready to bake, heat oven to 350 Deg F (180 C) and prepare baking sheets with parchment paper.
Scoop out balls of cookie dough, place a few inches apart on the baking sheet ( I bake six cookies at a time) smoosh down just a little, then sprinkle a few flakes of large flake salt on top.
Bake the cookies for 10-12 minutes until edges are golden and set but the middles still soft.
Cool in the pan for a couple minutes then transfer to a wire rack to cool completely. Repeat with the remaining dough, baking batches while others cool, until all are baked.
Store in an airtight container. Cookies can also be frozen once baked.