Preheat the oven to 350°F (175°C). Grease the baking pan or line it with parchment paper for easy removal.

In a large mixing bowl, whisk together the melted butter and sugar until well combined and smooth.

Add the eggs one at a time, mixing well after each addition, followed by the vanilla extract.

Stir in the sourdough starter until fully incorporated.

In another bowl, sift together the cocoa powder, flour, baking powder, and salt.

Gradually fold the dry ingredients into the wet mixture using a rubber spatula until just combined. Be careful not to overmix.

If desired, fold in the chocolate chips for added richness.

Pour the batter into the prepared baking pan, spreading it evenly.

Bake for 25 minutes or until a toothpick inserted into the center comes out with a few moist crumbs.

Allow the brownies to cool in the pan for about 10 minutes before transferring to a wire rack to cool completely before cutting.

For an extra indulgent treat, top the brownies with a dusting of powdered sugar or serve with a scoop of vanilla ice cream.

Store the brownies in an airtight container for up to 3 days at room temperature, or up to a week in the refrigerator.