Heat oven to 180C/160C fan/gas 4. Grease and line a large square traybake tin, about 28 x 28cm, with baking parchment. Put all the cake ingredients (apart from the cherries) in a large mixing bowl or tabletop mixer and beat together until thoroughly combined. Toss the cherries in a little flour, then fold them into the cake mixture using a spatula. Spoon the mixture into the prepared tin and bake for 30-35 mins until the cake is golden brown, springy to the touch, and a skewer inserted into the centre comes out clean. Leave to cool completely in the tin.
To make the icing, sift the icing sugar into a bowl, then add the lemon juice and enough water to make a thick yet fairly fluid icing. Transfer 3 tbsp of the icing to a small bowl and set aside. Spoon the remaining icing over the cooled cake – it should be liquid enough to level itself out; if not, use a knife to smooth it. Knead the marzipan to soften it, then incorporate enough red food colouring to turn it bright red. Roll into 48 cherry balls.
When the icing is almost set, place 2 balls directly next to each other on the icing, in rows of 4, with enough space between each to cut 24 equal pieces. Colour the reserved icing with green food colouring, then transfer to a piping bag fitted with a very fine nozzle, or simply snip off the end, and pipe cherry stalks next to the marzipan balls. When all the icing is completely set, take the cake out of the tin and cut into 24 pieces.