Brown 6 tablespoons of the butter in a small saucepan over medium heat. As soon as it is brown and fragrant, scrape it into a mixing bowl.
Add the remaining 6 tablespoons of cold butter to the brown butter, then stir in the mixed nut butter and the vanilla extract. Let stand so that the heat from the browned butter softens the cold butter. Give it a stir occasionally until mixture start to set.
While the butter mixture is setting, grab a big bowl and whisk together the flour, baking soda, baking powder, cream of tartar, salt and cinnamon until evenly blended.
Once the butter has cooled completely, using a big wooden spoon or scraper, beat in the brown sugar, granulated sugar and egg.
Add the flour mixture and stir until you have a soft dough.
Add chocolate chips and chunks (or wafers) and stir until blended. You can add them all at once, or hold some back and stick them in the formed dough rounds.
Divide dough into 10-12 equal size pieces and shape each piece into a round that's about 2 ½ inches and more like puck than a ball. Put in a zipper bag or on a plate with plastic wrap to cover, and chill for 48 hours. You can go ahead and bake one or two right away as well. I think they are very good baked immediately and better baked with chilled dough.
Bring however many dough balls you want to cook back to room temperature. You can bake them from cold as well, but they come out with more crinkles and crevices if you start them at room temperature.
Have your oven rack in the lower third of the oven and preheat oven to 350F.
Line a the larger baking sheet with parchment paper,
Place 4 of the rounds on the sheet, giving them plenty of space to spread. Sprinkle Maldon salt on top of the cookies.
Bake for about 15 to 18 minutes or until brown around the edges. There should be cracks throughout the top. Cool slightly on cookie sheet for about 3-5 minutes, then slide parchment onto a cool surface. Carefully transfer to a wire rack to finish cooling.