1. Preheat oven to 350°F (175°C) and grease or line a 9-inch pan.

2. Cream butter and sugar until light and fluffy.

3. Add eggs one at a time, mixing after each addition.

4. Stir in vanilla extract and milk until combined.

5. In a separate bowl, whisk flour, baking powder, baking soda, and salt.

6. Fold dry ingredients into wet mixture until just combined.

7. Gently fold in sourdough discard until batter is smooth.

8. Fold in any optional add-ins if desired.

9. Pour batter into prepared pan and smooth the top.

10. Bake for 30–35 minutes or until golden and a toothpick comes out clean.

11. Cool in pan for 10 minutes, then transfer to a rack to cool completely.

12. Slice and serve warm or at room temperature.