Preheat the oven to 180ºC/175ºc fan.
Place 24 cupcakes cases in a cupcake tin.
In a stand mixer cream the butter at room temperature and sugars until pale and fluffy.
Add the eggs one at a time and mix together.
Mix in the yoghurt.
In a separate bowl, measure and sieve out the flour, bicarbonate of soda, salt and the mixed spices.
Sieve in the flour gradually and stop when the flour is evenly mixed in.
Finely chop up a bar of white chocolate and mix in to the cake mixture.
Divide the mix into the cupcake cases.
Bake for 10-15 minutes or until it's golden brown and a skewer comes out clean.
Mix up the buttercream in a mixer until light and fluffy.
Add the buttercream to a piping bag with a star nozzle.
Add swirls of buttercream and stud with a range of sprinkles.