Preheat oven to 350 and line a cupcake pan with the liners of your choice.  In a small bowl, sift together the flour, salt, and baking powder.  Sifting insures that the dry ingredients are evenly distributed, but you can mix them up with a whisk just fine.

In large bowl, mix the butter and oil until it is smooth.  Add the sugar gradually, creaming it with the butter and oil until it has completely dissolved.

Add the eggs to the wet ingredients and beat the mixture until it's fluffy, then add the vanilla extract to the egg/butter/sugar and mix thoroughly.

Begin to add your dry ingredients and milk to the creamed ingredients, alternating which one you add to the bowl.  You'll add a bit of the sifted ingredients, then a bit of the milk, etc, beating the mixture with each addition until it is smooth.

Fill cupcake liners about ½ full, and bake for 15-18 minutes, or until a toothpick inserted into them comes out clean.  Cool for 5 minutes, then remove cupcakes from pan and allow to completely cool on a wire rack before frosting.

Beat egg yolks together in a small bowl and set aside.  

In small saucepan, mix milk, cornstarch, and sugar until well combined and smooth.  Heat over medium heat until it begins to thicken and bubble.  Simmer for 2 minutes, then remove from heat.

Add some of the heated milk mixture to the beaten eggs, whisk together, then add the egg mixture the saucepan.  Return to heat and bring to a light boil for two minutes, stirring continuously, then remove from heat once more.

Stir in butter and vanilla and mix until smooth.  Allow to cool to room temperature before using.

Heat heavy cream and sugar over medium-low flame until nearly boiling.  Pour over chocolate chips and allow to sit for 5 minutes.  

Whisk chocolate and cream mixture until smooth.  Cool in fridge until stiff, at least 1 hour.

With a small, sharp knife, remove a cone-shaped piece of cake from the center of each cupcake.

Fill the center of each cupcake with pastry filling.  It's easier with a piping bag, but you can improvise by cutting a small bit from the corner of a plastic freezer bag.

Pipe chilled ganache over the tops of the cupcakes.  Keep chilled until ready to serve.