Day 1: In a large bowl, combine 1 cup sugar, 1 cup flour, and 1 cup milk. Cover loosely and let sit at room temperature.
Day 2-9: Stir the mixture once each day.
Day 10: Add 1 cup sugar, 1 cup flour, and 1 cup milk. Stir well.
Day 11-19: Stir the mixture once each day.
Day 20: Add 1 cup sugar, 1 cup flour, and 1 cup milk. Stir well.
Day 21-29: Stir the mixture once each day.
Day 30: The starter is ready to use. Preheat oven to 350°F (175°C). Grease a baking pan.
In a large bowl, combine 2 cups flour, 1.5 cups sugar, 1 cup oil, 3 eggs, 1 teaspoon baking powder, 1 teaspoon baking soda, 1 teaspoon cinnamon, and 1 teaspoon vanilla extract. Mix well.
Fold in 1 cup chopped nuts and 1 cup chopped fruit if using. Pour batter into prepared pan.
Bake for 1 hour or until a toothpick inserted into the center comes out clean. Let cool before serving.