Cut your butter into 4-6 chunks. In a small sauce pan (preferably stainless or with a light colored bottom), add your butter and place over medium heat.
As the butter melts, stir or swirl the pan gently. Once it has melted, the butter will foam and cook loudly. After that subsides, the milk fats will begin to brown. When they are a golden to medium brown, remove from heat immediately and pour into a bowl to cool for about 15-20 minutes.
Preheat your oven to 350°F. Line an 8x8 baking tin with parchment and/or baking spray, and set aside.
In a medium bowl, add flour, salt, baking soda, and cream of tartar and whisk together.In a small bowl, mix together cinnamon and granulated sugar for topping. If you like the mixture to be more or less cinnamon heavy feel free to adjust ratio. In a large bowl or the bowl of your stand mixer, add your cooled browned butter, and shortening and mix until combined.
Add your granulated and brown sugar. Cream together on medium for about 3 minutes until well combined.
Add your egg, egg yolk and vanilla, and mix until the eggs have been incorporated into the sugar mixture completely.
Add your dry ingredients to the wet, mix on low until dough just comes together. Do not overmix.
Spread your cookie dough into an even layer in your prepared baking pan.
Generously sprinkle your cinnamon sugar mixture over the top of your pan.
Place pan on the center rack of your oven, and bake for about 25 minutes.
Remove from oven, and allow cookies to cool for at least 20 minutes before slicing. Enjoy!
Store cookies in an airtight container for up to 5 days, but cookies are best enjoyed fresh.
