Vanilla Cupcakes
6 tbsp, unsalted butter
3/4 cups sugar
6 tbsp sour cream, room temperature
2 tsp vanilla extract
3 large egg whites, room temperature
1 1/4 cups all purpose flour
2 tsp baking powder
¼ tsp salt
6 tbsp milk
2 tbsp water

Pastry Creme Filling
2 egg yolks
6 tbsp sugar
1 1/2 tbsp cornstarch
1 cup + 2 tbsp  milk
1 tbsp salted butter
1 tsp vanilla extract

Chocolate Ganache
12 oz  semi sweet chocolate chips
2 tbsp light corn syrup
3/4 cup + 2 tbsp heavy whipping cream

Let’s Do This

1. Preheat oven to 350 degrees, and prepare cupcake pan with liners
2. Make ganache:   Put the chocolate chips and corn syrup in a large bowl. Bring the heavy cream to a boil, then pour over the chocolate chips. Allow to sit for 3-5 minutes, then whisk until smooth. Place the chocolate ganache in the fridge until completely cool and firm, 1-2 hours.
3. Make cupcakes:  In a large mixing bowl, cream butter and sugar together until light in color and fluffy, about 3-4 minutes. Do not skimp on the amount of creaming time.  Add sour cream and vanilla extract and mix until well combined.  Add egg whites in two batches, mixing until well combined after each. Scrape down the sides of the bowl as needed to be sure all ingredients are well incorporated. Combine dry ingredients in a separate bowl, then combine the milk and water in a small measuring cup.
   Add half of the dry ingredients to the batter and mix until well combined. Add the milk mixture and mix until well combined. Add remaining dry ingredients and mix until well combined. Scrape down the sides of the bowl as needed to be sure all ingredients are well incorporated.
4. Fill the cupcake liners about halfway. Bake for 15-17 minutes, or until a toothpick inserted comes out with a few crumbs.
5. Make filling:  Put the egg yolks in a medium sized bowl and gently beat them together. Set aside.  Add the sugar, cornstarch and milk to a large saucepan and mix until smooth.  Cook, stirring continuously, over medium-high heat until mixture begins to thicken and bubble.   Reduce heat to medium and simmer for 2 minutes. Remove from heat.   Add a little bit of milk mixture to the egg yolks and whisk together, then add egg mixture to milk mixture. This process ensures that you don’t cook the egg yolks.  Place the pan back on the heat and bring to a light boil. Allow to boil for 2 minutes, stirring continuously.   Remove from heat and add butter and vanilla extract. Stir until smooth, then set aside to cool to room temperature.
6. Once everything is cooled and ready, cut out the centers of the cupcakes. I used an empty pill bottle, but apparently there’s a cupcake corer on the market; you could also use a knife.
7. Divide the pastry cream between the cupcakes and fill in the centers.
8. Frosting  If you want to get fancy, pipe it on (once it’s hung out and chilled), or just ice as usual.  Either way, delish!
9. Store in fridge, and are good for 2-3 days.  Be sure to cover so as not to dry out!