Preheat oven to 350°F. Line a 9x9-inch metal baking dish with parchment paper, leaving an overhang for easy removal. Lightly spray parchment with nonstick cooking spray. Set aside.
Spread pecans on a baking sheet and toast 7 to 10 minutes until lightly golden. Cool, then roughly chop. Set aside.
In a microwave-safe bowl (or over a double boiler), melt butter and chopped chocolate together in 30-second bursts, stirring until smooth and glossy.
Whisk in granulated sugar and brown sugar until combined. (It will look grainy, and that's okay.)
Add eggs one at a time, whisking vigorously until glossy and thick. Stir in vanilla.
Fold in flour, cocoa powder, salt, and espresso powder (if using) gently with a spatula until just combined. Do not overmix.
Fold in ¾ cup chocolate chips and 1 cup toasted pecans. The batter will be thick.
Spread about ⅔ of the batter evenly into the prepared pan.
Dollop ½ cup caramel sauce in spoonfuls over the batter. Swirl gently with a knife or skewer to create pockets; do not fully mix.
Spread the remaining brownie batter over the caramel layer to cover.
Dollop the remaining caramel sauce on top in generous blobs. Scatter the reserved ¼ cup chocolate chips and remaining chopped pecans over the surface.
Bake 35 to 40 minutes, until edges are set, top is cracked and bumpy, and center is slightly soft but not wet. A toothpick inserted in a non-caramel spot should come out with moist crumbs, but no wet batter.
Allow brownies to cool completely on a wire rack for at least 2 to 3 hours so the caramel sets.
Drizzle cooled brownies with caramel sauce, warming it slightly if needed.
Lift brownies from the pan using the parchment overhang, slice into squares, and serve. Best slightly warm for gooey caramel pockets!