Whisk together the light brown sugar and 2 teaspoons of salt in a large bowl. Set aside.
Melt butter in a small saucepan over medium-high heat. Continue cooking, swirling the pan, until the butter is a dark golden brown and brown bits start collecting at the bottom of the pan, 5 to 7 minutes.
Once the butter is browned, immediately pour it over the brown sugar mixture. Whisk to thoroughly combine.
In the same saucepan as was used to brown the butter, combine ½ cup of milk with 3 tablespoons of the bread flour to make the tangzhong starter. Cook the mixture over low heat, stirring with a wire whisk or silicone spatula, until thickened and paste-like, 2 to 3 minutes.
Remove from the heat and transfer the tangzhong starter to the bowl with the sugar/butter mixture. Whisk to combine.
Add the eggs and vanilla extract. Whisk until the mixture is smooth.
Whisk the remaining flour with the baking powder and baking soda. Add to the sugar/butter mixture. Whisk to combine into a smooth dough.
Place the bowl, uncovered, in the refrigerator for 15 minutes to cool.
After 15 minutes, add the chopped chocolate and, if desired, the optional pecans. Stir to combine.
Cover the bowl with plastic wrap and refrigerate for at least 24 hours, up to 72 hours.
Remove the dough from the refrigerator about an hour before baking the cookies. (See Tip 6)
Preheat the oven to 350°F. Line a large-rimmed baking sheet with a silicone liner or parchment paper. Set aside.
For supersized cookies, scoop the dough into 80-gram portions; for smaller cookies, scoop the dough into 40-gram portions. For consistently shaped cookies, roll each piece of dough into a smooth ball before baking (See Tips 7 and 8)
Bake the supersized cookies for 18 to 22 minutes; bake the smaller cookies for 15 to 18 minutes.
Remove the cookies from the oven. Allow the cookies to sit on the baking sheet for 15 minutes before removing them to a wire rack to cool completely. (See Tip 9)
Yield: 18 supersized cookies or 36 smaller cookies. (See Tip 10)