Pre-heat the oven to 175ºC (350ºF).
Line an 8x8” (20cm x 20cm) pan with baking paper or foil.
Melt the butter and set to one side until it cools a little.
Then, beat in the sugar followed by the egg. Lastly, add the vanilla extract.
Sift the flour and baking powder together and then stir into the wet ingredients, just until combined.
Chop your Maltesers into small pieces and stir through the batter.
Pour into the prepared pan and bake for around 18-20 minutes.
Remove from the oven and allow to cool completely.