In a heatproof bowl, melt the chocolate over a pan of simmering water. Once the chocolate is melted, set it aside to cool.

In a small bowl, combine flour, cocoa powder, baking powder, salt and cinnamon.

In a large bowl, beat butter and brown sugar for about 2 minutes until the mixture is pale and fluffy. Add the eggs one at a time and vanilla extract and mix it well. Mix in the cooled, melted chocolate. On low speed, add the flour mixture in two batches, alternating with the milk. Wrap the dough in plastic and refrigerate it for at least 2 hours.

Preheat oven to 175°C. Line baking trays with parchment paper.

Take about two teaspoons of dough and form a ball between your hands. Roll the dough ball, first in the granulated sugar until coated, then in the icing sugar. Place the balls on the parchment paper, leaving about 4 cm space between the cookies. Bake the cookies for 15 minutes, until the surfaces of the cookies crack, but be careful not to overbake them. Let the cookies cool a bit before transferring to a wire rack.