Set the oven to 350°F (175°C). Arrange oven racks in the upper and lower thirds. Line two large baking sheets with parchment paper to prevent sticking and ensure even baking.

In a medium mixing bowl, combine the melted butter and the egg, ensuring the mixture is well blended. Add the brownie mix and stir until no dry streaks remain and the batter is smooth and thick.

Using a medium cookie scoop or a heaping tablespoon, portion the dough into mounds of approximately 1½ tablespoons each. Space the cookies at least 2 inches apart on the prepared baking sheets to allow for spreading during baking.

For added richness and texture, press 3 to 4 chocolate chips into the top of each cookie mound. Sprinkle lightly with flaky sea salt, if desired.

Bake for 11 to 12 minutes, rotating the baking sheets from top to bottom halfway through the process to promote even baking. The cookies are done when the centers are glossy but not wet.

Allow the cookies to cool on the baking sheet for several minutes before transferring them to a wire rack to cool completely. Serve warm for a soft, gooey texture or at room temperature for a chewier consistency.