To prepare the Pastry Cream: In a saucepan bring milk to a simmer over medium heat. In a medium bowl, whisk together the egg yolks, vanilla extract and cornstarch, until the cornstarch dissolve. While whisking, slowly add the hot milk to the egg yolk mixture.

Return to saucepan, add sugar and cook over medium heat. Add butter and keep stirring until the mixture is thick and bubbling. Remove from heat.

Pour the mixture through a fine strainer into another bowl, cool. Cover with plastic wrap and chill in fridge at least two hours.

In a medium bowl, mix butter with sugar until combine, add eggs one at a time with vanilla extract. Mix until smooth. Sift the dry ingredients, then add it to the eggs mixture into two stages with the milk. Whisk all together until a smooth cupcake batter.

Fill three quarter of cupcakes liner with the batter. Bake in preheated oven 180°C for 25 minutes. When out of oven let it cool on wire rack completly before fill.

For ganache: Place chocolate chips in another medium bowl with butter, pour hot cream over. stir together until smooth chocolate ganache.

Cut off the surface cupcakes top with a sharp knife. carve a deep hole in the middle of cupcakes, with a help of teaspoon remove the core. Pipe pastry cream inside, cap the cream with the reserved cupcake plug.

Spooning ganache over the top of the cupcakes.

Better to chill for 1 hour before serving it.