A glorious sponge cake that cuts into slices revealing the Union flag. The pattern is assembleld like a jig-saw and each section needs to be cut precisely so it all fits together neatly. It's much easier if the cakes are made a day or so before they are cut.
- For the sponge:
- 700g unsalted butter
- 700g caster sugar
- 12 large free-range eggs, at room temperature, beaten
- 4 tsp vanilla extract
- 700g plain flour
- 3 tbsp baking powder
- about 125ml milk, at room temperature
- navy and ruby edible food colouring gels
- For the butter icing:
- 375g icing sugar, sifted
- 120g unsalted butter, at room temperature
- 2 1/2 tbsp milk
- 1/2 tsp vanilla extract
- To finish:
- 1 x 370g jar apricot jam, sieved and warmed
- 1kg marzipan
- 1kg white ready-to-roll sugar paste icing
- 250g Royal icing sugar
- 3 brownie pans or cake tins, 30 x 20 x 5cm, greased and lined with baking paper
- a piping bag fitted with a 2mm tube
1. Preheat the oven to 180c/350f/gas 4. Unless you have a large free-standing electric mixer it will be easier to make the sponge mixture in 2-3 batches. Beat the butter and sugar together with an electric mixer until creamy. Gradually beat in the eggs, followed by the vanilla. Sift the flour and baking powder, then add to the mixture in 2 batches, beating on a low speed. Add the mild and fold in using a large metal spoon.
2. Weigh 350g of the mixture and put into another bowl. Tint it a deep red. Transfer to one of the prepared tins and spread evenly - the mixture will be about 1cm deep. Bake for about 15 minutes until a cocktail stick inserted into the centre comes out clean. Leave in the tin for 5 minutes, then turn out onto a wire rack to cool completely.
3. Colour the rest of the sponge mixture navy blue, then divide between the remaining 2 tins, spreading evenly; the mixture should be about 3cm deep. Bake 30-40 minutes until a cocktail stick inserted into the centre of each sponge comes out clean, then cool as before. If possible, wrap the cooled sponges in foil or clingfilm and leave for a day before assembling the cake.
4. Make the butter icing by beating the ingredients together until very smooth and spreadable; add more milk if necessary. Cover and keep at room temperature.
5. Carefully trim the blue sponges so they are exactly 3.5cm high. From each blue sponge cut 2 strips exactly 6cm wide and 30cm long (you will have cake left over). Using an electric carving knife or a bread knife, cut each blue strip diagonally and lengthways to make 2 long triangular pieces of sponge cake 6cm wide x 3.5cm high: to make your diagonal cut, start from the top right-hand edge of the strip and slice down to the bottom left-hand edge.
6. Trim the red sponge, if necessary, so it is 1cm high. Cut the red sponge into 3 strips: 2 strips each 3.5cm wide and 30cm long, and the third piece 13cm wide and 30cm long.
7. Spread a thin layer of butter icing over the centre of a large rectangular cake board to anchor the sponge, then start to build - see the photo for guidance here (if in doubtdo a dry run without the butter icing to make sure it all fits in place). Set a blue triangle on the board, 6cm side down, with the 3.5cm side close to the centre. Spread a thin layer of butter icing on the sloping top cut surface. Spread both sides with butter icing and set it upright against the 3.5cm side of the blue triangle. Set another blue triangle against the red strip on the side with butter icing. Invert 2 more blue triangles on top of the 2 already on the board and press them all gently together.
8. Spread the top surface of the assembled cake with a thin layer of butter icing, then set the wide strip of red sponge on top to cover it and press down gently. Spread this red sponge with butter icing, then repeat the pattern on top using the remaining blue triangles and red strip. Looked at from the end, you will see a Union flag design. Press everything together gently with your hands, then trim with a long knife to make sure the sides are straight. Brush off loose crumbs.
9. Brush the warm jam over the cake. Roll out the marzipan to a rectangle large enough to cover the cake, then carefully drape it over the cake and smooth it with the palm of your hand. Trim off the excess marzipan.
10. Roll out the icing in the same way. Lightly brush the marizpan with cooled boiled water so it is just sticky, then cover with the white icing as you did for the marzipan. Press it on gently, then smooth and polish it with the palm of your hand. Trim off the excess.
11. Mark a cross of St George on the icing using a pin and a ruler to prick out straight lines. Mix the Royal Icing sugar with about 2 tbsp water to make a smooth icing that can be piped. Tint it red. Spoon it into the piping bag and pipe decorative swirls within the marked lines of the cross. Leave to set before cutting.