These are great-imagine, a Boston cream pie you can eat in one (maybe two) mouthfuls! I overcooked the glaze a little bit, hence the slightly gritty look, but otherwise they were delicious. The cupcakes are sturdy, almost like a pound cake, and filled with delicious pastry cream, which I could eat by itself. Here is a very easy recipe for pastry cream. You will need:
1 2/3 c heavy cream
3 egg yolks
1/4 cup sugar
1 1/2 teaspoons vanilla (more if you want a strong vanilla flavor, or you could use a vanilla bean)
3 teaspoons cornstarch
2 tablespoons butter, cut into 4 pieces
Put the cream into a small pot and put it over medium heat. While it heats, whisk the egg yolks, sugar, and salt. If you're using the vanilla bean, cut it open and scrape out the seeds. Put the seeds into the cream and throw in the vanilla bean (you'll remove it later). Put the cornstarch into the egg yolk mixture and whisk until it's pale and thick.
Let the cream come to a simmer. There will be small bubbles forming on the edges of the cream but it shouldn't be quite boiling. Take the cream off of the heat but leave the stove on. Carefully pour a little hot cream into the egg mixture while whisking to temper it. Add the rest of the cream in a slow stream while whisking.
Return the mixture to the pot and put it back over the heat. Whisk for a minute or two until the cream becomes thicker and shiny. (When the cream coats the back of a spoon you dip into it, it's done. If you overcook it it will still be good, it'll just be pudding.) Take it off the heat and add the vanilla extract (if using), then the butter. Whisk until melted. If you used the vanilla bean, remove the bean halves.
Put the pastry cream into a bowl and press a piece of plastic wrap directly on the surface (this prevents it from getting a skin as it cools). Let it cool in the fridge for at least two hours. You can then put it into an airtight container.