Preheat the oven to 180C/350F and place one large muffin liner into a muffin tray OR place 2 normal cupcake liners into a cupcake tray.
Place the butter and sugar into a medium sized bowl and beat with an electric hand mixer until light and fluffy, around 45 seconds on medium speed. Add in the vanilla and egg white, then mix until smooth and well combined, around 30 seconds.
Add in the flour, baking powder, salt and milk and mix on medium speed until everything is smooth and combined. Don't beat the batter too much, just make sure it's well mixed and there are no lumps. Add in the funfetti, if using, and fold in with a spoon so you don't break the funfetti into bits.
If you're making two normal sized cupcakes: fill the liners 2/3 of the way and place in the oven for 14-16 minutes, until risen, golden and an inserted skewer into the centre comes out clean.
If you're making one large cupcake/ramekin - place the batter into your liner, filling it 2/3 of the way, or fill your ramekin 3/4 of the way. Place in the oven for 18-22 minutes, until risen, golden and an inserted skewer into the centre comes out clean.
Leave the cupcake/s to cool completely before frosting. Take 3-4tbsp of shop bought butter cream icing and place into a small piping bag with an open nozzle attached. Pipe a swirl onto your cupcake/s and finish with some more funfetti, if desired.
You can also make your own glaze with 4tbsp icing sugar and a splash of milk if you don't want to use buttercream frosting. Make the glaze in a shallow bowl and then dunk the top of your cupcake in to coat. Sprinkle with funfetti and leave to set for 15 minutes.
Birthday Cupcakes will keep at room temperature, in an airtight container, for 4 days.