Preheat oven to 350 °F (175 °C). Line a 9×9-inch pan with parchment paper, leaving edges to lift out.

In a bowl, whisk together flour and granulated sugar. Cut in ¾ cup softened butter until mixture resembles coarse crumbs. Press firmly into the bottom of the prepared pan to form the shortbread crust.

Bake crust for about 15 minutes, until lightly golden. Remove from oven.

Meanwhile toast pecans on a sheet in the oven at 300 °F for 4 minutes or until fragrant, then scatter evenly over warm crust.

In a small saucepan over medium heat, combine brown sugar and ⅔ cup butter. Stir constantly until mixture reaches a boil, then continue boiling one full minute without stirring. Remove from heat and carefully pour caramel over pecans and crust.

Return pan to the oven and bake 13–20 minutes, until caramel bubbles around edges.

Remove from oven and immediately sprinkle chocolate chips over top. Let sit 2–3 minutes to melt, then swirl gently with a knife to create a smooth layer. Optionally, sprinkle sea salt.

Cool completely (at least 30 minutes; chill for firmer texture), then lift out using parchment and slice into squares.