In a medium saucepan over low heat, combine ¼ cup unsalted butter and ⅓ cup light brown sugar. Stir until the butter melts and the mixture bubbles. Whisk in ½ cup heavy cream, cooking for an additional 2-3 minutes until thickened. Stir in ¼ teaspoon flaky sea salt and set aside to cool.

In a large mixing bowl, cream together ¾ cup softened unsalted butter, ¾ cup brown sugar, and ¼ cup granulated sugar using an electric mixer on medium speed for about 2 minutes until light and fluffy. Add 1 large egg and 1 teaspoon vanilla extract, mixing until smooth.

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

Carefully fold the cooled caramel into the cookie dough, allowing chunks of caramel to remain for delightful swirls. The dough should be sticky and rich.

Preheat your oven to 350°F (175°C) and line a baking sheet with parchment paper. Drop generous portions of dough onto the prepared sheet, spacing them 2 inches apart. Sprinkle lightly with flaky sea salt. Bake for 10-12 minutes until the edges turn golden.

Allow cookies to cool on the baking sheet for about 5 minutes, then transfer to a wire rack to cool completely before serving or storing in an airtight container.