Rhubarb Upside-Down Buttermilk Cakelets

I've done it again.... I've joined another group: Have the Cake. Every month one of the members picks a recipe for a cake, cookie, cracker, pie, bar, biscuit or brownie. Everyone can make it as is or put their own spin on it. You have the whole month to complete it and when you are done, you post your baking experience on your blog and on Have the Cake's blog! Each participant gets to pick a recipe for an assigned month and it should be something they've never made before. This month it was Gerri's turn to pick a recipe, she choose Buttermilk Cake for our May Challenge.

• 
  
• 
  
• 
• 
  
• Last Saturday I went to the market and bought 2 kilos of rhubarb, with the intention to use part of it for this challenge. I happened upon this wonderful Rhubarb Upside-Down Cake and decided to adapt it by subbing the milk with buttermilk, however I forgot to buy buttermilk. So I used the advice Gerrie gave us and made my own buttermilk by adding one tablespoon of lemon juice to one cup of milk and let it sit for 10 minutes until it clabbers. I used my non-stick 6 hole-baking pan for buns, fairy cakes, muffins & yorkshire puddings. Doesn't that cake look nice and fluffy?
• 
  
• 
  
• 
• 
  
• Rhubarb Upside-Down Cakelets
• makes 12 3-inch cakelets
• recipe adapted from Taste of Home
• 
  
• Ingredients
• 2/3 cup packed brown sugar
• 3 tablespoons butter, melted
• 2-1/4 cups diced fresh or frozen rhubarb
• 4-1/2 teaspoons sugar
• 
  
• Batter:
• 6 tablespoons butter, softened
• 3/4 cup sugar
• 2 eggs, separated
• 1 teaspoon vanilla extract
• 1 cup plus 2 tablespoons all-purpose flour
• 1-1/2 teaspoons baking powder
• 1/2 teaspoon salt
• 1/4 cup buttermilk
• 1/4 teaspoon cream of tartar
• Whipped cream, optional
• 
  
• Directions
• Butter the baking pan and line the bottom of each individual hole with parchment, butter the parchment. In a small bowl, combine brown sugar and butter. Spread into the baking pan. Layer with rhubarb; sprinkle with sugar. Set aside.
• 
  
• In a large bowl, cream butter and sugar until light and fluffy. Beat in egg yolks and vanilla. Combine the flour, baking powder and salt; add to creamed mixture alternately with buttermilk, beating well after each addition.
• In a small bowl, beat egg whites and cream of tartar on medium speed until stiff peaks form. Gradually fold into creamed mixture, about 1/2 cup at a time. Gently spoon over rhubarb (pan will be full, about 1/4 in. from the top of pan).
• 
  
• Bake at 325° for 25 minutes or until cake springs back when lightly touched. Cool for 10 minutes before inverting onto a serving plate. Serve warm with whipped cream if desired.
• 
  
•