Preheat the oven to 190°C (170 fan/ 375F/ Gas 5) and line 3 baking sheets with baking paper.
Cream together the softened butter and sugars in a mixing bowl until pale and fluffy. You may prefer to use an electric mixer - this cookie dough gets quite stiff later on!
Beat in the egg and vanilla extract.
Mix in the flour, cocoa powder, bicarbonate of soda and baking powder. The mixture will seem quite stiff and dry at this point but you need to keep mixing. By hand, it takes about 5 minutes to get it to come together. Don't forget you can always use an electric mixer to make life easier (I quite like the work-out!).
Mix in the crushed mini eggs, micro eggs and white chocolate chips.
Take heaped tablespoons of the mixture and roll into balls. Place on the prepared baking sheets, well-spaced. The mixture makes 20 cookies. Use a cookie scoop to ensure the cookies are the same size!
Bake in the oven for 10-12 minutes. Half-way through baking, take the baking sheets out of the oven and flatten down the cookies with a fish slice or palette knife. Return to the oven to carry on baking.
Once out of the oven leave to cool for 10 minutes before placing on a wire rack.