For a healthier variation, substitute the vegetable oil with melted coconut oil or applesauce, and consider reducing the brown sugar to ½ cup.
Optional mix-ins include omitting the raisins or walnuts, or replacing them with chopped pecans, almonds, dried cranberries, or golden raisins.
Store in an airtight container at room temperature for up to 3 days. For longer storage, freeze for up to 2 months, wrapping each muffin individually in plastic wrap and placing them in a sealed container. Defrost in the refrigerator before serving.