Preheat your oven to 160C Fan / 180C and prepare a cupcake / muffin tin with cases.
Place all your sponge ingredients into a large mixing bowl and whisk until well combined and thoroughly mixed (1 minute should do it). If making chocolate cupcakes, don't forget to reduce the flour measurement and replace it with sieved cocoa powder - see the ingredients list above for measurements.
Divide the mixture between the cases. I fill mine just over 2/3 full.
Place in the oven for about 22 minutes. To check if the cupcakes are cooked, insert a skewer and if it comes out clean, it's done!
Allow the cupcakes to cool completely on a cooling rack.
For the buttercream:
For the buttercream, place your softened butter into a bowl of a stand mixer and mix on a medium speed for about 5 minutes until the butter has gone a lot paler in colour. You can also do this by hand using a silicone spatula, but you'll need to mix for longer!
Add your icing sugar gradually. I add it in 2-3 stages and beat for about 3 minutes between each addition. Start mixing slowly to save your kitchen from a real icing sugar mess, but then increase the speed to medium / high for each of your 3 minutes.
Add your vanilla extract and mix once more.
Split your buttercream into 3 separate bowls equally. Colour each with a different colouring gel (using concentrated gel means you only need a drop or two - refrain from using liquid colourings).
For assembly of the cupcakes:
Once the cupcakes are cool, if you wish to have a jammy (bloody!) centre, use something circular (like the wide end of a metal piping nozzle) to make a small hole and spoon a little jam into the centre. This is only optional though.
Spoon your different coloured buttercream into three piping bags with grass piping tips (linked above in the FAQ section) or any tip you fancy, if you don't have one. Then pipe your buttercream on top - use different colours however you wish - I used contrasting colours for the base and eyebrows.
Finish with edible eyes.