Chocolate Buttons Cake recipe

i'm crazy about chocolate and
 i like all the recipes which 
contains it and this is one 
of them i can't tell you how
 much it's delicious.
ingredients:
For Cake
150g butter (softened)

135g sugar
3 eggs
200g self-raising flour
6 tbsp milk (the batter still quite dry even with 6 tbsp of milk)
55g cocoa powder

For filling
180g chocolate (melted) -- I still left quite an amount of melted chocolate, 150g should be more than enough
method:
1. Preheat oven at 180C (I used 170C for my oven), grease the donut trays.
2. Whisk butter, sugar, eggs, milk and flour and cocoa until smooth and well-mixed.
3. Transfer batter into piping bag. Pipes batter onto donut trays till full. (I used spoon to scoope the batter into the donut tray instead)
4. Bake for about 18 to 20 minutes or until well risen and springy to the touch. (I baked 18 mins but over baked, so 15 mins for my oven)
5. Transfer to a wire rack and let cool.
6. Double-boil chocolate. Pipe into the hole in each donut-shaped cakes. (I used spoon to fill)
http://bakericious.blogspot.com/2012/07/chocolate-buttons-cake.html