In the bowl of your stand mixer add the butter, brown sugar, and granulated sugar and beat to combine well. Beat until fully mixed, about 3 minutes.
Add the egg and vanilla and beat to combine, scraping down the sides as needed.
Add the sourdough starter and mix until just combined.
Sprinkle the baking powder, baking soda, and salt into the bowl. Add the flour. Mix to combine.
Add the chocolate chips and stir to combine.
Scoop a heaping tablespoon of the cookie dough onto a baking mat or parchment paper lined baking sheet. Space the cookies about 2 inches apart.
Bake until the cookies are golden brown, about 10 minutes.
Let the cookies cool on the pan for 1-2 minutes before removing to finish cooling on a wire rack.
Repeat with remaining cookie dough.
Store extra cookies in an air-tight container.
Notes
I prefer to use my bubbly active starter for this recipe because my kids don't like the sourdough tang in the cookies (I think it's really pleasant, my husband thought I added lemon!).
If you like the tang, use your sourdough discard. If you are neutral, I'd start with using your mature starter to see how that goes first.