Preheat the oven to 350 degrees. butter and flour a 25 cm tube pan with a nonremovable bottom.
In a large bowl, sift together the flour, baking powder, baking soda, and salt. In a medium pot, combine the sugar and water and bring them to a boil. Remove the pot from the heat and stir in the chocolate and 1 stick of butter. When the chocolate and butter have completely melted, whisk the mixture to combine completely. Whisk in the beaten eggs. Pour about half the chocolate mixture into the dry ingredients and whisk vigorously to thoroughly combine the ingredients and remove any lumps. Working quickly, add the remaining chocolate mixture and whisk to combine.
Pour the batter into the prepared pan and bake for about 60 minutes, until a cake tester inserted in the center comes out clean. Let the cake cool in the pan for about 15 minutes, then turn out onto a rack to cool completely.
In a medium bowl, cream together the remaining 3 sticks of butter and the confectioners sugar, until light and fluffy. Remove one third cup of the icing, place in a small bowl, and color it with a few drops of the green food coloring. Put the remaining icing in a pot, add the vanilla. Over low heat, stir the icing until it becomes a pourable consistency. (If it overheats, causing the butter to spearate, put the icing in the refrigerator to chill and stir to bring it back together.) Pour the icing over the cooled cake so that it drips down the center and outside. Cluster the red berries in groups of 3 on top of the cake. Fill the green icing into a pastry bag fitted with a leaf tip and pipe a few leaves around each cluster of berries.
Serves dozen to 16.