Put the caster sugar, oil and egg in a bowl. Whisk together.
Sift in the flour, icing sugar, baking powder and cocoa powder. Stir together just as much as it takes to get an even dough.
Divide the cookie dough into ten equal pieces.
Press a piece of dough into a disc, then place a mini creme egg in the centre. Wrap the dough around a mini creme egg, rolling into a ball. Place the ball on the lined tray. Repeat until all the dough balls have a creme egg in the centre.
Put a little icing sugar in a bowl and roll each ball in it to lightly coat, then return to the tray.
Bake the cookies for 10-12 minutes. They should form natural cracks as they bake.