Preheat the oven to 180C/350F and line a 12 hole cupcake tray with liners.
Place the butter/marg and sugar into a large bowl, or the bowl of your stand mixer and beat on medium-high speed until light and fluffy, around 2 minutes.
Add in the eggs and vanilla extract, scraping down the sides as necessary, and beat until well combined and smooth, around 1 minute on medium-high speed.
Add in the flour, baking powder, nutmeg and salt if using and mix on low until the mixture just starts to come together, then add the eggnog and alcohol, if using.
Continue to mix on low-medium speed, until your mixture is smooth and well combined.
Divide the mixture between your liners, filling each liner ¾ full. I use a 2tbsp cookie scoop to ensure even cupcakes.
Place in the oven for 18-22 minutes, until risen, lightly golden and an inserted skewer into the centre comes out clean.
Transfer to a wire rack to cool as soon as possible to ensure cakes don’t peel away from the liners.
Once completely cool, make the frosting: Place butter and vanilla extract into a large bowl and beat until light and fluffy.
Add in the nutmeg, salt, a little icing sugar and a little eggnog. Mix until the sugar starts to combine. Continue to gradually add icing sugar and eggnog, mixing in between each addition until you have a light and fluffy frosting.
Half fill a piping bag fitted with an open star nozzle and pipe a swirl onto each cupcake. Sprinkle each cupcake with a little nutmeg.
Eggnog Cupcakes will keep in an airtight container, in the fridge for 3 days.