Break or grate the marzipan into a large bowl and beat in butter, sugar, eggs and almond essence until light and fluffy. Beat in the flour and salt. Split batter into three equal portions, mixing one portion with green food colouring, one with yellow, and one with red. Spread each portion out to 1/2cm thickness into the bottom of an ungreased 20x30cm baking dish.
Bake each layer for 12 to 15 minutes in the preheated oven, until lightly browned. Allow to cool.
Once the layers have cooled, spread the tops of the first two layers with raspberry jam. Press all the layers together then spread melted chocolate over top of the third layer. Chill in the refrigerator 1 hour, or until jam and chocolate are firm. Slice into small rectangles to serve.