• In a medium bowl, whisk together the flour, cocoa powder, baking soda, and salt. Set aside.
• In the bowl of a stand mixer fitted with the paddle attachment (or a separate bowl and hand mixer), cream together the butter and brown sugar on medium speed.
• Add the egg, sourdough starter, and vanilla extract and continue to mix until smooth.
• With the stand mixer set to low speed, slowly pour the dry ingredients over the wet ingredients. Mix until just fully combined.
• Use a rubber spatula or wooden spoon to stir in the chocolate chips.
• Bake immediately or cover and chill the dough in the refrigerator for 1 hour, or up to 3 days.

When Ready to Bake

• Preheat oven to 350℉.
• Line a large baking sheet with parchment paper. Use a spoon or cookie scoop to roll the cookie dough into approximate 1¼ inch sized balls.
• Place on the prepared cookie sheet spaced 2 inches apart. Gently press 2-3 of the remaining chocolate chips on the top of each cookie dough ball.
• Bake in preheated oven for 12-14 minutes. The cookies will appear cooked around the edges and slightly soft and gooey in the centers.
• Allow to cook 5 minutes in baking tray before transferring to a wire rack to cool completely. Sprinkle with flaky sea salt if desired.