Combine chunks of chocolate and butter in medium saucepan. Place over lowest heat possible and stir until melted and smooth. (Or place chocolate and butter in top of double boiler over simmering water; stir mixture as it melts until it becomes smooth). Remove from heat. Cool chocolate mixture to lukewarm.
Sift the flour, baking powder, cinnamon, and salt into a small bowl. Mix together with a spoon to distribute everything evenly.
Using a stand mixer (or handheld mixer), beat the eggs and 1 1/2 cups of sugar in a large bowl, until they are pale and quite thick, around 8 minutes. Mix in the melted chocolate, working quickly as the mixture will start to solidify. Sprinkle half of the dry ingredients over and quickly fold in. Follow with the last of the dry mixture, incorporating it completely into the batter. Dough may be very stiff.
Cover the bowl with plastic wrap and refrigerate for at least one hour, until it is firm enough to scoop. (I let my dough refrigerate overnight.)
Preheat the oven to 350 degrees F. Place powdered sugar in large shallow bowl. Line two large baking sheets with parchment paper.
Scoop dough into portions of about 2 tablespoons each and roll into balls that come out around 1 1/2 inches in diameter. Roll each ball in powdered sugar and then place on lined baking sheets, leaving about 2 inches between the unbaked cookies.
Bake for 12-15 minutes, until the tops are cracked and the cookies are just firm to the touch. Move the baking sheets to a cooling rack and allow to sit for 5 minutes. Transfer cookies to separate cooling rack and cool to room temperature.