Preheat the oven at 350 degrees. Line two baking sheets with parchment paper.

Combine flour, cocoa, baking soda and salt in a large bowl. Leave aside.

Pour some water in a medium sized dish and put on a medium heat. Put pieces of chocolate in a smaller dish, and place it on the larger dish with water in it (it must not touch the water) and stir until the chocolate melts. Leave it aside to cool.

Combine softened butter and sugar in a medium sized bowl using electric hand mixer, adding one egg at a time. Mix it well for a couple of minutes using maximum speed, until it becomes creamy.

Add melted chocolate and vanilla and stir until well combined.

Combine the mixture with the dry ingredients and stir until well combined.

Finally, add chocolate chunks and leave it for 5 minutes to rest.

Drop the dough on a baking pan lined with parchment paper. Make sure to leave about 2 inch space between the cookies.

Bake for 11 minutes.

Leave them to cool and enjoy them for a couple of days.