Preheat oven to 350°F (175°C). Line a 9×13-inch baking pan with aluminum foil or parchment paper, leaving an overhang on the sides for easy removal. Lightly grease the foil or parchment.
For the crust: In a large bowl, whisk together flour, powdered sugar, salt, and cinnamon (if using).
Add the cold cubed butter and cut it into the flour mixture using a pastry blender or two knives until the mixture resembles coarse crumbs.
Press the mixture firmly and evenly into the bottom of the prepared pan.
Bake the crust for 15 minutes until lightly golden. Remove from oven but keep the oven on.
While the crust is baking, prepare the filling: In a large bowl, whisk together eggs, corn syrup, sweetened condensed milk, vanilla extract, brown sugar, and salt until well combined.
Stir in the chopped pecans and chocolate chips.
Pour the filling over the warm crust, spreading it evenly.
Return the pan to the oven and bake for 30-35 minutes, or until the filling is set around the edges but still slightly jiggly in the center.
Remove from the oven and let cool completely at room temperature, about 2 hours.
For best results, refrigerate for at least 1 hour after cooling to make cutting easier.
For the optional topping: Melt 1/2 cup chocolate chips in the microwave in 30-second intervals, stirring between each, until smooth. Drizzle over the cooled bars and sprinkle with flaky sea salt if desired.
Use the foil or parchment overhang to lift the bars out of the pan. Cut into squares with a sharp knife, wiping the knife clean between cuts for neat edges.