Pre-heat the oven to 375F / 160C
First, you want to melt the solid dark chocolate and butter together using a double broiler. You probably do not have one of these. Not to worry- you can fashion one. Boil some water in a saucepan, set a glass bowl on top, and the steam will heat the bowl enough to melt the chocolate and butter without it getting too hot, as it would if you applied direct heat. Or, you could use a tiny saucepan and hold it within a larger one just above the water line. Whatever works with your own kitchen equipment!
Once the butter and chocolate is all melted, pour into a mixing bowl. Add the sugar, eggs and vanilla and mix (ideally using an electric mixer) until it is all combined.
In a separate bowl, sift together the flour, cocoa powder, baking power, and salt
Gradually add the flour mixture to the bowl, mixing as you go, until a soft dough is formed.
Fold in the chocolate chunks to complete the dough.
Now, using an ice cream scoop, portion the dough onto baking trays. Flatten a little, and press in as many mini eggs as you can. The cookie will spread when you bake it, and the mini eggs will disperse, so try and fit as many on now as you can.
Bake for 15 minutes. The cookies will start to look all crackly, but will probably seem too soft. But it is OK- they are done! They continue to cook and harden after you take them out of the oven.
Allow to cool before removing from the baking sheets.