Preheat the oven to 350 degrees F (175 degrees C). Lightly grease baking sheets, or line them with parchment paper.
Cream sugar and butter in a large bowl. Beat in sourdough starter and egg.
Stir in flour, baking powder, vanilla extract, salt, and baking soda until smooth.
Drop dough by teaspoonfuls onto the prepared baking sheets.
Bake in the preheated oven until edges are golden, 10 to 12 minutes.
