Preheat oven to 350° F. Cream butter with sugar and 2 Tbsp brown sugar until fluffy. Beat in eggs, orange zest and vanilla. Stir in buttermilk. In a separate bowl, sift together flour, baking soda and salt. Add flour to butter mixture and incorporate. Spoon batter evenly between 12 greased muffin cups. Place 2 plum wedges in the centre of each cake and press gently, so as not to press plum all the way to the bottom of tin. Sprinkle tops of plums with remaining 3 Tbsp brown sugar and bake for 15 to 20 minutes, until cake is golden brown around the plum. Cool for 10 minutes before removing from tin.
Yield: 12 baby cakes.