First, make the cookies. Preheat the oven to 325F / 160C

Mix together the flour, cocoa powder, baking soda and salt in a bowl. Set aside.

Melt the dark chocolate using a double boiler or a heatproof bowl set on top of a pan of boiling water.

Transfer the melted chocolate to a large mixing bowl. Beat in the sugar, eggs and vanilla, with an electric mixer (or you could do it by hand if you put some work in!). Once incorporated, add the flour mixture bit by bit (trying not to get it all over yourself and the all over the kitchen surfaces when you first start mixing it in!). Finally, fold in the chocolate chunks.

Scoop our the dough and roll between your hands to make balls about the size of golfballs or a little bigger if you prefer a larger cookie. Flatten slightly and place on baking sheets.

Bake for 15 minutes, until the surfaces are starting to crackle. Remove from oven and leave to cool completely.

Meanwhile, you can make the frosting.

Using electric mixers, beat the butter, cream cheese, vanilla and brown sugar together until it starts to go fluffy. Add in the flour and salt, a little at a time, until incorporated. Finally, add in the powdered sugar (a little at a time) and beat until the frosting is fully mixed and fluffed. If you prefer yours more stiff, add additional powdered sugar but we preferred to keep ours a little creamier. Finally, stir in the chocolate chips.

To assemble, spoon frosting onto the bottom side of a cookie and spread it around with the back of the spoon. Once covered, press another cookie (bottom side down) over the frosting to seal them together.