Mini Plum-Raspberry Upside-Down Cakes

I love to make single-serving desserts. It probably has something to do with the fact that I'm cooking for just two and that I don't like having partial-cut cakes on my countertop (there's just not enough room). Here's my latest endeavor from Saturday night. These cakes are based on a 2001 recipe from Martha Stewart Living. It would also be tasty with apples or pears and cranberries, I think. Maybe I'll try that at Thanksgiving. (The pan I used is a jumbo muffin pan that has six muffin cups.)

Mini Plum-Raspberry Upside-Down Cakes

3/4 cup (1 1/2 sticks) butter
Brown sugar
3 plums, halved and pitted
1/2 pint raspberries
3/4 cup granulated sugar
1 tsp. orange zest
1 tsp. vanilla
3 egg yolks
1 1/2 cups all-purpose flour
1 tsp. cinnamon
3/4 tsp. baking powder
1/4 tsp. baking soda
1/4 tsp. salt
1/4 tsp. freshly grated or ground nutmeg
1/2 cup sour cream

1. Melt 1/4 cup butter. Evenly pour butter in lightly greased jumbo muffin cups. Sprinkle 1 to 2 Tbsp. brown sugar over butter. Place 1 plum half, cut side down, in center of each muffin cup. Arrange about 6 raspberries around outside of each plum half.
2. Beat remaining 1/2 cup butter and 3/4 cup granulated sugar at medium speed with an electric mixer until light and fluffy. Beat in orange zest and vanilla. Beat in egg yolks, 1 at a time, beating until blended after each addition.
3. Combine flour and next 5 ingredients. Add half of flour mixture to butter mixture, beating until blended. Beat in sour cream; then add in remaining flour mixture. (Note: Batter will be very thick.) Spread batter evenly over plums in muffin cups.
4. Bake at 375° for 40 to 45 minutes or until cake is done. Use a fork to carefully remove cakes from pan. Place on individual serving dishes, plum sides up. Serve warm.