Preheat oven to 350°F. Generously grease an 8-inch by 8-inch glass or metal baking pan.
In a medium bowl, combine flour, brown sugar, cinnamon, baking soda and salt. Mix well. Stir in raisins.
In another medium bowl, combine unfed discarded starter, cold water, vinegar, vanilla extract and olive oil. Stir in shredded carrots.
Add wet ingredients to dry ingredients. Stir until moistened and pour batter into prepared pan.
Bake for 25 to 30 minutes or until a fork inserted in the center of the cake comes out clean. Cool the pan on a baking rack.
If frosting the cake, allow it to cool completely first.