Line a 9 x 9 inch baking pan with parchment paper, leaving some to overlap two sides. Preheat oven to 350 degrees.
Melt butter with sugar and brown sugar in a microwave-safe bowl in 30 second increments, stirring in between, until smooth. Let cool 5 minutes. Then, whisk in the vanilla and eggs. Add the cocoa powder, flour, espresso powder, and salt. Stir until just combined. Fold in the mini chocolate chips with a spatula. The batter will be thick. Or "thicc" as the kids say nowadays.
Spread the brownie batter evenly into the prepared pan. Bake 20 minutes.
While the brownies bake, make the pecan filling. Stir together the brown sugar, maple syrup, melted butter, bourbon (if using), cinnamon, and vanilla. Beat in the egg. Fold in pecans.
Once the brownies finish their first bake, pour the pecan filling overtop and gently distribute across the batter. Bake an additional 15-20 minutes until a toothpick inserted into the center comes out with just a few moist crumbs.
Let brownies cool 5 minutes in the pan, then carefully lift the overlapping parchment and set onto a wire rack. Cool 10 minutes or longer. Slice (this will be messy!) and serve.