Ingredients
- 150g self-raising flour
- 150g caster sugar
- 150g salted butter, softened plus extra for the tin
- 3 at room temperature eggs, beaten
- ½ heaped tsp baking powder
- 2 unwaxed lemons, zested
- 2 oranges, zested
- orange food colouring gel
- yellow food colouring gel
ICING
- 70g salted butter, softened
- 180g icing sugar, plus extra for dusting
- 3 sprigs thyme, leaves stripped and finely chopped
- 1 unwaxed lemon, ½ zested and 1½ tsp of juice
- 1 orange, zested and 1½ tsp of juice
- 300g white marzipan
Method
- Heat the oven to 180C/fan 160C/gas 4 and butter the sides and bottom of a 20cm square tin. Cut a 20cm × 40cm piece of baking parchment and the same of foil. Butter the foil and then put the baking parchment on top so that they’re stuck together.
- With the foil-side facing up, fold in half widthways like a book, then open out, turn over and push up the centre fold to make a 4cm pleat, that sticks up, down the centre.
- Line the base of the tin with the foil-side down, ensuring the pleat is uppermost and is dead in the centre of the tin, to create 2 identical rectangles within the tin. Ensure the paper-lined foil is pushed into all the corners of the tin with a slight overhang on either side.
- Put the flour, sugar, butter, eggs and baking powder in a bowl and whisk until just combined. Divide the mixture between two bowls. Whisk the lemon zest into one plus enough colouring to make a strong custard colour. To the other, add the orange zest and enough colouring to make quite a bright orange colour.
- Spoon each mixture into seperate halves of the tin. Make sure the divider is straight before smoothing the surface of each.
- Bake in the oven for 25 minutes until the cakes have risen and are springy to the touch. Allow to cool for a few minutes before turning out onto a cooling rack and removing the divider.
- Meanwhile, make the icing by beating together the butter, icing sugar, thyme, zest and juice until fluffy and smooth.
- Trim the brown off long edges of the cakes and then cut each cake into 3 lengthways, ensuring all 6 strips are the same size and shape so that the cross section of each is a square.
- Put a lemon, orange and then another lemon strip next to each other and use the icing to stick them together. Spread some more icing over the top and then stick the 3 remaining strips on top, alternating them in a chequerboard effect icing in-between them and on top.
- Roll the marzipan out, on a clean worksurface dusted lightly with icing sugar, to a rectangle 20cm × 30cm or the same length as the cake and 4 times its width with a little extra to trim away.
- Invert the cake onto the marzipan, iced-side down and 2cm in from the edge. Spread the remaining icing over the rest of the cake, apart from the chequerboard ends.
- Carefully roll up the cake in the marzipan and seal where the marzipan joins. Trim any ends off to neaten.
- Put the cake, seal-side down on a plate. Crimp the two top edges and score a diamond pattern on the top using the back of a knife before serving.