Whisk 1/2 cup melted unsalted butter, 3/4 cup packed brown sugar, and 1/4 cup granulated sugar until glossy. Whisk in 1 large egg and 1 tablespoon vanilla extract until smooth.

Stir 1 1/2 cups all-purpose flour, 1/2 teaspoon baking soda, and 1/4 teaspoon salt into the butter mixture just until no dry streaks remain. Fold in 1 cup bittersweet chocolate chips.

Press half of the finished chocolate chip cookie dough evenly into the prepared 8x8-inch pan, taking the dough to the corners without packing it hard.

Place 20 chopped soft caramels and 2 tablespoons heavy cream in a small saucepan. Warm over low heat, stirring often, until completely smooth. Remove from the heat and stir in 1/2 teaspoon flaky sea salt.

Spread all of the salted caramel over the cookie dough base, leaving a 1/4-inch border around the edges.

Crumble the remaining half of the chocolate chip cookie dough over the caramel in small pieces. Do not press the top flat.

Bake the filled 8x8-inch pan at 350°F for 24 to 30 minutes, until the edges look golden and set while the center remains softer.

Cool the bars completely in the pan for at least 2 hours. Lift out the slab with the parchment, sprinkle with extra flaky sea salt if desired, and cut into 12 bars or 16 smaller squares.