Preheat oven to 350F. Line a 9x13-inch pan with parchment, leaving overhang for easy removal. Lightly grease any exposed pan.

In a large microwave-safe bowl, combine butter and 8 oz of the chocolate chips. Microwave in 30-second bursts, stirring between each, until melted and smooth. Let cool 5 minutes so you don't scramble the eggs.

Whisk sugar into the cooled chocolate mixture until glossy. Add eggs one at a time, whisking well after each, then stir in vanilla. Fold in flour, cocoa powder, and salt until just combined. Fold in remaining 4 oz chocolate chips. Spread evenly in prepared pan and bake 25 minutes until top looks set but still soft in center.

While brownies bake, combine corn syrup, brown sugar, butter, bourbon if using, vanilla, and salt in a medium saucepan. Bring to a boil over medium heat, stirring constantly. Boil 2 minutes until slightly thickened. Remove from heat and stir in pecans until evenly coated.

Remove brownies from oven and immediately pour pecan mixture over top, spreading to cover evenly. Return to oven and bake 15-20 minutes more until topping bubbles vigorously and looks caramelized. Cool completely in pan on a wire rack, at least 1 hour, before lifting out and cutting into squares.