To make the frosted leaves and cherries, whisk the egg white with a fork until frothy. Tip the sugar onto a plate. Brush the egg white onto the bay leaves or dip them, then sprinkle the sugar over the leaves and half the cherries to coat. Leave to dry on a sheet of parchment for 6 hrs or until the frosting has completely dried.
Heat the oven to 180C/160C fan/gas 4. For the sponge, butter and line a 30 x 20cm traybake tin with parchment. Beat the butter and sugar together in a large bowl with an electric whisk until creamy. Whisk in the eggs, one by one, then sieve in the flour, spices and baking powder. Fold in the yogurt, vanilla and chocolate chips. Tip into the tin, smooth over and bake for 30-35 mins until the sponge is golden and springs back when pressed. Leave to cool in the tin for 10 mins, then turn out onto a wire rack, remove the parchment and leave to cool completely.
Reduce the oven to 120C/100C fan/gas ½ and leave the door open briefly to make sure the temperature drops low enough. To make the meringues, whisk the egg white in a large bowl with an electric whisk, or in the bowl of a stand mixer with the whisk attachment, until stiff peaks form. Continually whisking, add the sugar, 1 tbsp at a time, until it’s completely combined. Once it’s all added, beat for another 3-4 mins until you get a stiff, shiny meringue. Transfer the mixture to two small piping bags fitted with star and round nozzles. Use a cocktail stick, knife or spoon dipped in the food colouring to paint the inside of the bags in stripes up the length, painting each bag with a different colour (see pic A) and leaving the area nearest the nozzle uncoloured, then fill with meringue. Cover a baking sheet with parchment, using a little of the meringue on the underside to stick it to the tray. Pipe blobs onto it, well spaced apart, to make meringue kisses – they will come out plain first (pic B). Bake for 30 mins, then turn off the oven and leave the meringues inside to cool to room temperature. Decorate them with gold leaf or glitter, if you like.
Press the jam firmly through a sieve to remove any large chunks and stir what’s left in the sieve back into the jar. Stir in a few pinches of glitter, if you like, then transfer to a piping bag fitted with a small round nozzle.
Beat the buttercream ingredients together using an electric whisk until you get a pale, fluffy icing. Transfer to a large piping bag with a wide, round nozzle.
To cut the sponge into a tree shape, first split the cooled cake into two layers using a cake cutter or serrated knife (pic C). Using a ruler or a sheet of baking parchment the same width as the cake, mark a halfway point at the top end of the cake (pic D). At the bottom end of the cake, mark it into thirds (pic E). Using these as a guide, cut squares from the bottom end of the cake, leaving a centre section for the tree stump, then cut from your middle mark at the top down to the bottom edges to create a Christmas tree shape (pic F). Use the off-cuts to make cake pops, or in trifle. Carefully lift off the top sponge using a baking sheet, and pipe blobs of buttercream all over, starting from the outside edge (pic G). Chill for 20 mins to firm up. Pipe some of the jam between the buttercream blobs, except the outer edge.
Position the remaining cake on top (pic H), and pipe more icing blobs all over (pic I). Add the frosted leaves, frosted and plain cherries, ginger biscuits (see our recipe) and meringues (pic J), sprinkle a little glitter over the un-frosted cherries, and pipe on the remaining jam in blobs (pic K). Add the biscuits, putting a star-shaped one at the top, and add gold leaf, if you like. Will keep, well covered in the fridge, for two-three days.