Divide the butter in half (113 grams per half). Cut into cubes.
Add half the butter (113 gras/half cup) into a saucepan over medium-medium high heat. Melt the butter while gently whisking. After the butter has fully melted, continue whisking. It will bubble and froth. After about 5-10 minutes, it will start to turn an amber color and give off a nutty aroma. Remove the browned butter from the heat. Let cool for about 10-20 minutes. Optionally, sift the flecks out of the butter. If some get in, that's ok.
In a medium bowl whisk together the flour, baking soda, cinnamon and salt. Set aside.
In a large bowl beat the remaining ½ cup (113 grams) of butter (the butter that has not been browned) with the brown sugar and granulated sugar until no lumps of butter or sugar remain.
Beat in the cooled browned butter, followed by the vanilla extract and eggs.
Starting with the mixer on a low speed, beat the dry ingredients into the butter mixture.
Stir in the chopped dark chocolate and pecans. I always leave a little out of the batter for adding on top of each cookie.
Cover the bowl with plastic and refrigerate for 30 minutes or up to 24 hours.
Form the dough into balls about 1.5 tablespoons in size and place 2 inches apart on the lined cookie sheet.
When ready to bake, preheat the oven to 350F (180C or 170C fan forced) degrees. Line cookie sheets with parchment paper or silicone baking mats.
Form the dough into balls with about 3 tablespoons of dough each. I use 2 scoops of a medium cookie scoop (each scoop is 1.5 tablespoons). If the dough has been in the fridge overnight, you may need to let it sit for 10 minutes on the counter first so that it's easier to work with.
Place the dough balls at least 2.5 inches (about 5 cm) apart on the lined cookie sheets. Optionally, place a few extra chocolate chunks and pecan pieces on top of each cookie.
Bake 1 sheet at a time in the middle of the preheated oven for about 10-13 minutes, or until the tops look just set apart from the pools of melty chocolate.