Preheat the oven to 350, line a muffin tin with muffin cups. Cream together the butter, sugar, egg and vanilla in a large bowl with an electric or stand mixer.
Add the flour, baking powder and salt. Fold in by hand, then finish mixing with the mixer to avoid a dust bath! Pour batter into muffin cups, filling half way. Gently shake pan to even out and remove air bubbles.
Bake for about 15 minutes or until golden brown and a toothpick inserted comes out clean.
Allow to cool completely.
The cream:
In a large bowl, whip the butter and smooth & creamy. Add the cinnamon, nutmeg, egg nog and half the powdered sugar. Whip with an electric mixer until smooth. Add the remaining powdered sugar gradually while mixing.
Note* if your cream is too thin, add more powdered sugar. Cream should be fluffy
Spoon cream into a pastry bag with a tip in place. Insert the tip into the cupcake and gently squeeze until you see the filling start to rise. Frost the cupcake while you are there and then continue filling and frosting the remaining cupcakes!
Serve with, what else... eggnog!