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1. Preheat over to 350 degrees and line pans with cupcake liners.
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2. Sift cake mix into a small bowl to remove any lumps and set aside.
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3. In a large bowl, gently whisk oil, egg whites, buttermilk and sour cream together.
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4. Split your vanilla bean the long way and use the tip of your knife to scrape out the inside. Add this to your wet ingredients and stir in. (Or simply add your vanilla extract.)
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5. Stir in cake mix until fully incorporated.
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6. Fill cupcake liners 3/4 full and bake for 15-20 minutes, or until and inserted knife comes out clean.
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7. Lemon Curd: Using a double boiler (or a make shift one), whisk eggs and sugar together. Add lemon juice, butter and lemon zest and stir constantly over medium heat for about 15 minutes. The mixture should coat the back of a spoon. Let cool.
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8. Blueberry Buttercream: Beat butter for 2 minutes and scrape down bowl. Add mashed blueberries (strain your berries if you plan on using a star piping to, you don't want it to get clogged!). Slowly add powdered sugar until you reach your desired consistency. Depending on your berries, the buttercream might not be a very rich color, add a little food dye to fix that.
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9. Once your cupcakes have cooled, use a knife to cut a little cone out of the top of each cupcake. Fill the holes with your cooled lemon curd and top with your buttercream.