Cream butter and sugars together in a mixing bowl.
Add applesauce and vanilla, beating until fluffy.
In a separate bowl, combine dry ingredients and add to sugar mixture alternately with milk.
Stir in plums and walnuts, if desired.
Spread into a greased 13 x 9 baking pan or a loaf pan and bake at 350 F or 160 C for about 35 minutes (a loaf pan may require slightly longer) or until a toothpick inserted near the centre comes out clean.
Serve as is, or with a dollop of whipped cream on top.