In a medium bowl, whisk together the all-purpose flour, baking soda, and salt. Set aside.

In a large mixing bowl, combine the slightly cooled melted butter, granulated sugar, and packed light brown sugar. Beat with an electric mixer on medium speed for 2-3 minutes, until light and fluffy.

Add the sourdough discard, room temperature egg, and vanilla extract to the butter mixture. Beat again on medium speed until just combined, scraping down the sides of the bowl as needed. The mixture might look slightly curdled; this is normal.

Gradually add the dry ingredients to the wet ingredients, mixing on low speed until just combined. Be careful not to overmix; stop as soon as no streaks of flour remain.

Fold in the chocolate chips using a rubber spatula until evenly distributed throughout the dough.

Cover the bowl with plastic wrap and refrigerate the dough for at least 1 hour. Chilling helps the flavors meld, prevents spreading, and results in a chewier cookie. For best results, chill for 4-24 hours.

Preheat your oven to 375°F (190°C). Line two baking sheets with parchment paper.

Using a 1.5-2 tablespoon cookie scoop, drop rounded balls of dough onto the prepared baking sheets, leaving about 2 inches between each cookie. You should get 8-10 cookies per sheet.

Bake for 10-12 minutes, or until the edges are golden brown and the centers are still slightly soft. They may look underdone, but they will continue to set as they cool.

Remove the baking sheets from the oven and let the cookies cool on the sheets for 5 minutes before transferring them to a wire rack to cool completely. This helps them maintain their soft, chewy texture.