Melt the chopped dark chocolate with butter on a double boiler. Mix well both ingredients to combine. Set aside to cool.
Beat the eggs with the sugar until they double their volume.
In a medium bowl, combine the ground walnuts, chocolate chips, flour, and baking powder.
Add the mixture to the eggs alternating with the melted chocolate.
The mixture has to look uniform in color and texture.
Grab an ice cream scoop, or a tablespoon and form cookies, then place them on a cookie baking tray covered with parchment paper.
Bake them at 350F/180C for 12-15 minutes maximum, just enough for the cookies to get a shiny look. Make sure you don't overbake them. The center should still be soft.
Remove the tray from the oven and let the cookies sit on the tray for a few minutes until they cool down. Place them on a cooling rack to cool down completely.
They keep well in an airtight container for up to 2 weeks. Freeze the baked cookies for up to three months.