Follow these concise steps to create your delectable Boston Cream Pie Cupcakes:

For the Cupcakes:

1. Preheat your oven to 350°F (175°C) and line a cupcake pan with 12 cupcake liners.
2. Mix Dry Ingredients: In a bowl, whisk together the flour, baking powder, and salt.
3. Cream Butter and Sugar: In a separate large bowl, cream the softened butter and sugar until light and fluffy.
4. Add Eggs and Vanilla: Beat in the eggs one at a time, followed by the vanilla extract.
5. Combine Mixtures: Gradually add the dry ingredients to the wet mixture, alternating with the milk. Mix until just combined.
6. Fill Liners: Distribute the batter evenly among the cupcake liners, filling them about two-thirds full.
7. Bake: Place in the oven and bake for 20-25 minutes, or until a toothpick comes out clean.
8. Cool: Remove from the oven and let them cool in the pan for about 10 minutes before transferring them to a wire rack to cool completely.

For the Pastry Cream Filling:

1. Heat Milk: In a saucepan, heat the milk over medium heat until it’s steaming but not boiling.
2. Whisk Yolks and Sugar: In a bowl, whisk together the egg yolks and sugar until pale.
3. Add Cornstarch: Sift in the cornstarch and continue whisking until smooth.
4. Temper Eggs: Gradually pour in the hot milk while whisking to temper the eggs.
5. Cook Mixture: Return the mixture to the saucepan and cook over medium heat, whisking constantly until thick.
6. Add Butter and Vanilla: Remove from heat, then stir in the butter and vanilla extract. Transfer to a bowl, cover with plastic wrap, and refrigerate until cold.

For the Chocolate Ganache:

1. Heat Cream: In a small saucepan, heat the heavy cream until it starts to simmer.
2. Combine with Chocolate: Pour the hot cream over the chocolate chips in a bowl and let it sit for a couple of minutes.
3. Stir Until Smooth: Stir until the chocolate is completely melted and the ganache is smooth. Let it cool slightly before using.

Assembling the Cupcakes:

1. Core the Cupcakes: Use a paring knife to cut out a small circle in the top of each cupcake, creating a hole for the filling.
2. Fill with Cream: Spoon or pipe the chilled pastry cream into the hole of each cupcake.
3. Top with Ganache: Spoon or drizzle the chocolate ganache over the filled cupcakes, allowing it to cover the top completely.