01 - Preheat oven to 350°F. Line a 9x13-inch baking pan with parchment paper, leaving an overhang for easy removal.
02 - Whisk together flour, baking soda, salt, and ground cinnamon in a medium bowl; set aside.
03 - In a large bowl, whisk melted butter, brown sugar, and granulated sugar until smooth. Add eggs and vanilla extract, mixing thoroughly.
04 - Gradually fold dry ingredients into wet mixture until just combined, avoiding overmixing.
05 - Fold in chocolate chips and nuts, if using, ensuring even distribution.
06 - Evenly spread dough into prepared pan and sprinkle flaky sea salt on top if desired.
07 - Bake 23 to 27 minutes until edges are golden and center is set but still slightly soft for a gooey texture.
08 - Allow bars to cool in pan for at least 20 minutes before lifting out and slicing into 12 bars.