Preheat the oven to 180°C (350°C) and line and grease two 20cm round cake tins.
Beat the butter and caster sugar until light and fluffy.
Add the eggs and Greek yoghurt and beat until smooth.
Add in the malted milk powder, flour, cocoa, baking soda and baking powder and mix until just combined.
Pour half of the chocolate cake mix into each of the cake tins and spread in an even layer.
Place in the oven for 20-25 minutes. Insert a skewer at 20 minutes and if the skewer comes out clean the cakes are cooked.
Allow them to cool completely before icing them.
While the cakes cool, make the malted buttercream.
Place the softened butter in a bowl and beat until smooth.
Add in the malted milk powder and beat.
Add in half the icing sugar and a tablespoon of water and beat.
Add the remaining icing sugar and add more water as needed.
You want a thick, smooth consistency.
Crush the Maltesers.
Spread 1/2 - 2/3 of the buttercream on top of one of the cakes. (How you pipe and decorate is up to you). Pour over half of the crushed Maltesers. Place the second cake on top and then spread the Malteser Chocolate Spread over the top leaving an inch around the sides.
Pipe the remaining malted buttercream around the edge. Pour the remaining crushed Maltesers in the middle and top with as many Maltesers you like.
You can omit the Malteser Chocolate Spread and replace with other chocolate spreads, chocolate ganache or more malted buttercream.I used these disposable piping bags and this piping tip.