Heat oven to 180ºC/160ºC fan-assistant. Line 1-2 muffin tins with 15 muffin cases.
Melt the butter in a small saucepan or in the microwave (check on it every 10 seconds if using the microwave) and let it cool a little.
Transfer the melted butter to a bowl and add the yogurt, eggs and vanilla. Beat until combined.
Sift the flour, sugar, ground almond and baking powder into a large bowl. Add the zest. Stir to combine them and make a well in the centre.
Pour in the wet ingredients into the centre of the dry ingredients. Mix well until lump-free.
Spoon the mixture into the muffin cases. Each case should not be more than 2/3 full.
Bake in the oven for 25-30 mins or until a knife or toothpick inserted into the centre comes out clean. Transfer to a wire rack to cool completely.
Making the Frosting
Start by beating the butter in your mixer (I used my Smeg) until it’s fluffy (about 5 minutes, starting with lower power). Then add half the icing sugar and combine well, and then add the rest of the sugar and combine well again. If the mixture becomes too thick, you can add 1-2 tablespoon of milk to loosen it.
Divide the buttercream into bowls and add the colours of your choice to each bowl. I like to start by adding just a couple drops and building up from there so my colours don’t get too crazy. Mix the colours well into the buttercream.
Place each colour of buttercream into a piping bag, twisted at the top, with a nozzle of your choice. You are ready to pipe now!
Onto each cupcake, you can pipe simple rosette shapes or more complicated flower designs depending on your nozzles.