1Make up the basic sponge mixture in 3 batches, using an electric hand-mixer. Bake in 1 x 15cm, 1 x 20cm and 1 x 23cm round cake tins.
2When cool, halve the cakes. Sandwich back together with the frosting and raspberry jam.
3Put the large sponge on a plate. Measure its height and cut 3 wooden skewers to that length. Repeat with the medium sponge.
4Cut a circle of thin, clean card the size of the medium sponge and place under it. Repeat for the small sponge.
5Push the first 3 skewers into the large cake, 4cm in from the edge, to form the points of a triangle. This will support the weight of the top two cakes so they don’t squash it! Repeat with the other 3 skewers and the medium cake.
6Brush the large sponge with apricot jam. Dust a work surface with icing sugar, roll out half the white icing to 3mm thick, cover the sponge and trim.
7Put on a plate. Wrap the trimmings in clingfilm. Repeat with the rest of the icing, to cover the other sponges. Allow to dry, then stack in 3 tiers.
8Roll out the green, yellow, blue and red icing – don’t mix the colours – and cover each with clingfilm when done. Cut into 3cm-wide strips. Mark lines with a knife about 1cm apart, to look like book spines, then cut into smaller sections. Stick to the sides of the cakes with royal icing, like rows or stacks of books on shelves.
9Mix some white icing with a little red to get pale pink, and use to model Matilda’s head and hands, and her legs, bent at the knee. Use blue icing for her body. Allow to dry completely, then assemble her on the cake, sticking her in place with royal icing.
10Place her legs so they’re dangling over the edge of the middle tier, then add her body, with her back against the top tier.
11Stick on her head and hands, then add her hair, made from orange royal icing, and black icing eyes and a red mouth.
12For the loose books, wrap coloured icing covers around white pages. Arrange on the cake tiers, with an open book on Matilda’s lap. Allow the icing to dry, then serve.