Set the oven to 180 degrees. Melt half of the chocolate together with butter. Beat eggs with honey for a minute or with an electric whisk. Stir in the chocolate and butter, as well as the milkshake and beat a little more. Mix coconut flour, cocoa, baking powder and vanilla in a separate bowl and finally fold this into the batter. Take out a tray and cover with baking paper. Lay out the batter. Chop up the rest of the chocolate and sprinkle over the cake. Bake in the oven for about 10-15 minutes.