Preheat oven to 350°F and line a cupcake pan with cupcake liners.

In mixer, cream butter and sugar together 4 mins,

Add sour cream and vanilla extract and mix.

Add whites and combine well.

Combine dry ingredients in a separate bowl.

In a measuring cup, combine milk and water.

Add half the dry ingredients to the mixer.

Then add the milk/water and finish with the rest of the dry.

Fill cupcake liners halfway and bake 15-18 mins.

Cool

Put yolks in a bowl and whisk.

Put sugar, cornstarch and milk in a saucepan and cook on medium until starts to thicken while stirring constantly.

Lower heat and simmer 2 minutes then remove heat.

Add a little of this to the yolks stirring so the yolks don't cook.

Add the mixture all back into the pot and bring to a gently boil.

Cook 2 mins while stirring.

Remove heat and stir in butter/vanilla. Cool.

Boil the cream and pour over the chips/corn syrup in a heatproof bowl.

Cover and let sit a few mins and then whisk.

Chill 2 hours until completely cool.

Cut out centers and fill with pastry cream. Replace top with a small piece of cake you cut out.

Pipe on the ganache!

Ateco tip 844 is the best! Even better than my Wilton 1M!

Store in fridge.