Preheat oven to 180 degrees C. Lightly butter a fluted tart tin with a removable base.
Sift the flour into a bowl with the chocolate powder and almond meal. Add the icing sugar and cardamom and mix well. Put into a food processor, add the diced butter and mix 1 minute or until the dough forms a ball.
Spread the dough in the tart tin using your hands. Smooth with the back of a spoon. Prick all over with a fork and chill in the fridge for 10 minutes.
Bake 25 minutes. Remove from the oven and immediately slice into wedges while soft. Let cool 15 minutes in the tin, then remove the outside of the tin and cool on a rack.