Preheat your oven to 350 degrees Fahrenheit (F). Prepare an 8x8-inch baking pan by lining it with parchment paper, ensuring that it hangs over the edges slightly for easy removal later. Lightly spray the parchment paper and any exposed parts of the pan with non-stick spray, then set it aside.

In a saucepan over medium heat, add the unsalted butter and melt it until it turns a beautiful golden brown color, producing a fragrant nutty smell. Keep an eye on it as it can quickly go from browned to burnt if not monitored closely.

Once browned, remove the saucepan from heat and allow it to cool for a few minutes before scraping the butter into a large heat-proof mixing bowl. Whisk in the light brown sugar until well combined, then stir in the bourbon and vanilla extract.

After mixing in the brown sugar, add in one large egg along with an additional egg yolk at room temperature, beating until fully incorporated into the mixture. Next, use a rubber spatula to fold in all-purpose flour, ground cinnamon, and salt until just combined without overmixing.

Gently fold in the toasted pecans and chocolate chunks using your spatula until evenly distributed throughout the batter. Scrape the batter into your prepared baking pan, smoothing out the top with your spatula for even baking.

Place your pan in the preheated oven and bake for approximately 24 minutes or until you see firm golden edges while maintaining a slightly wobbly center. Once baked, let them cool in the pan for at least one hour before cutting them into squares; sprinkle with flaky sea salt before serving if desired.