Preheat oven to 180C/160C fan force. Line a 12 muffin pan with patty pan liners.
Place the butter, sugar, milk, egg, vanilla, cinnamon, FATE mix and custard powder in a large bowl. Use electric beaters on low speed to beat until combined. Gradually increase the speed to high and cream mixture for 5 min, until pale, creamy and smooth.
Spoon mixture evenly into the patty pan liners and bake in oven for 20-25 min. When cakes are firm to touch remove from oven and cool in tin for 5 min.
Remove muffins to a wire rack. Melt extra butter and brush the top of each muffin with the melted butter whilst muffins are still warm.
Combine extra sugar and cinnamon and sprinkle over the top of each buttered muffin.
Serve the muffins while still warm and enjoy.