Preheat oven to 350°F / 180°C. Place the melted butter, salt, brown sugar and molasses in a bowl and whisk until thick, smooth and creamy.
Add the eggs (one at a time), whisking well between each addition. Follow with the egg yolk and whisk it into the mix well. Whisk in the vanilla.
In a separate bowl, sift the flour, baking powder, and the spices.
Add the sifted dry ingredients to the wet ingredients in 3 additions, alternating with 2 additions of the milk. FOLD THEM INTO the batter - do not over beat.
Line a regular cupcake tray with cupcake liners.
Fill all 12 cupcake liners with the cake batter (about ⅔ - ¾ way up) and bake in preheated oven for 15 - 20 minutes, until the cupcake tops are slightly springy to the touch.
Take the cupcakes out of the oven, and let them cool down completely.
Eggnog Pastry Cream
Place the milk and white chocolate in a small saucepan and heat over medium heat to melt the chocolate. Stir frequently to make sure the chocolate melts.
Whisk the egg yolks with the corn flour (corn starch) until smooth.
Temper the egg yolks with a little (about ¼ cup) of the hot milk mix. Make sure to whisk the egg yolks consistently to avoid them from turning into scrambled eggs.
Add the tempered egg yolks back into the rest of the hot milk mix and whisk to combine.
Add the cinnamon and nutmeg and whisk the custard over medium heat to mix well.
Whisk frequently while cooking the custard until it has thickened, and the mixture starts to break the surface with a “blop”.
Remove the custard from the stove and pour it into a bowl. Cover it with plastic wrap (with the plastic wrap touching the surface to prevent a skin from forming), and let it cool down completely. This custard will be a very thick paste once it cools down.
Once the custard has cooled, add half of the whipped cream into the eggnog custard and fold it in to combine. Add the rest of the cream and fold it in to mix well and distribute evenly.
The pastry cream can be stored in a piping bag and refrigerated until needed.
Cream Cheese Frosting
Place the butter and cream cheese in a stand mixer bowl and using a whisk attachment, whisk until the butter and cream cheese mix is light and fluffy.
Add the salt and vanilla, and whip to combine.
Add confectioner's sugar in batches and mix on low speed until well combined. Scrape the sides to make sure the frosting is mixed properly.
Whip the frosting on medium-high speed until light, fluffy and creamy.
If you prefer a softer frosting, add the cream and whip the frosting for another minute.
Place the frosting in a large pastry bag with an open star tip (or any pastry tip you like).
Assembly
Using a melon baller, carefully remove a small half sphere from the center of the cupcakes (see photo in blog post).
Once all the cupcakes have a hollow center, fill it with eggnog pastry cream.
Pipe the cream cheese frosting on top.
Optional - drizzle some molasses on top, or sprinkle some cinnamon or gold dust on top, or decorate with mini gingerbread cookies. Enjoy!