In a medium saucepan over medium heat, melt ¼ cup of unsalted butter. Stir in ⅓ cup of packed light brown sugar and allow to bubble gently. Whisk in ½ cup of heavy cream, stirring for 2-3 minutes until thickened. Stir in ¼ teaspoon of flaky sea salt and let cool.

In a large mixing bowl, cream together ¾ cup of softened unsalted butter, ¾ cup of packed light brown sugar, and ¼ cup of granulated sugar until light and fluffy (3-4 minutes). Add in 1 room temperature large egg and 1 teaspoon of pure vanilla extract, mixing until incorporated.

In a separate medium bowl, whisk together 2 ¼ cups of all-purpose flour, 2 tablespoons of cornstarch, ½ teaspoon of baking soda, and ¼ teaspoon of fine sea salt. Gradually add to the wet mixture until just combined.

Gently fold in the slightly cooled caramel sauce into the cookie dough until evenly distributed, scraping up any caramel settled at the bottom.

Preheat oven to 350°F (175°C) and line a baking sheet with parchment paper. Drop rounded balls of dough onto the prepared sheet and bake for 10-12 minutes until edges are golden. Sprinkle with flaky sea salt after baking.

Allow cookies to cool on the baking sheet for a few minutes before transferring to a wire rack. Optionally, drizzle warm caramel sauce over the cookies before serving.