These beautiful bars are the smartest confectionery you will ever make – they are very rich and sweet. Try filling them with whipped double cream instead of marshmallow and serve them up as a dessert.
First, make the shells. Melt 300g of the white chocolate in a bowl set over a pan of gently simmering water. Add a little pink food colouring to give the desired shade then, using a pastry brush, paint a layer of chocolate inside 12 moulds. Chill for 15 minutes, to set. Reserve the remaining melted chocolate.
Make the biscuit dough. Beat the butter and sugar in the bowl of a stand mixer fitted with the beater, on medium speed for about 5 minutes, until pale and creamy. Add the egg yolk, flour, almonds, baking powder, salt, mahleb (if using), and vanilla and almond extracts. Mix on a low speed until the mixture forms a stiff dough. Wrap the dough in cling film and freeze for 15 minutes, until firm enough to roll. Measure the base of a buche-mould hollow, then use the card to cut a template to the size for each biscuit base.
While the dough is in the freezer, heat the oven to 190°C/170°C fan/375°F/Gas 5. When the dough is ready, roll out on a lightly floured work surface to a rough rectangle about 6mm thick. Cut the dough into 12 rectangles using the template. Place the biscuits on the lined baking tray and bake for 10–12 minutes, until golden brown around the edges. Remove from the oven and trim as necessary to neaten the edges, making sure each biscuit will fit snugly into each mould later on. Set aside to cool on the tray.
Coat the moulds with another layer of pink chocolate and return to the fridge.
Make the jam. Place the raspberries in small pan, mash with a fork, then add the sugar. Place over a medium heat, bring to the boil, then cook, stirring, for about 4 minutes, until thickened. Skim any foam from the top, then spoon the jam into a bowl and stir in the almond extract. Allow to cool completely, then spoon into the small piping bag.
To finish the shells, toast the almonds in a dry pan for 2–3 minutes, then place them in a small bowl and crush with the end of a rolling pin until finely broken up. Allow to cool, then scatter evenly into each chilled chocolate shell in the mould.
Make the marshmallow. Pour 100ml of water into a bowl and sprinkle over the powdered gelatine. Allow it to sponge (absorb the water). Heat the sugar and liquid glucose in a small pan with another 100ml of water over a low heat until the sugar has dissolved. Bring to the boil and boil until the syrup reaches 120°C/248°F on a sugar thermometer, then add the sponged gelatine and stir to dissolve.
Whisk the egg white in the clean, grease-free bowl of a stand mixer fitted with the whisk, on medium speed until frothy. Pour the sugar syrup down the side of the bowl in a very thin stream, whisking continuously, until the meringue is thick and glossy. Whisk in the almond extract, then place the marshmallow into the large piping bag and leave to cool for 10 minutes, or until it is thick enough to hold its shape when piped.
Snip the end of the large piping bag and pipe a line of marshmallow on top of the almonds in each hollow. Snip the end of the small piping bag containing the jam and pipe a line of jam on top of the marshmallow. Top each with a biscuit. (You will have lots of marshmallow left over – see the tip below for how to use it.)
Melt another 100g of the white chocolate in a bowl set over a pan of simmering water. Tint this chocolate pink to match the first batch and spoon it evenly over each hollow to flood and cover the filling. Scrape off any excess with a palette knife, then return the mould to the fridge for 30 minutes to 1 hour to set.
When the bars are set, turn them out onto a wire rack placed over a sheet of baking paper. To decorate, mix a tiny drop of blue food colouring with the alcohol. Dip the small paintbrush into the blue colouring and splatter each biscuit.
Mix together the gold lustre and popping candy in a bowl and set aside. Melt the remaining 50g of white chocolate. Colour it with a drop of orange food colouring. Dip in the remaining small cake-decorating paintbrush and paint a line of chocolate on each bar. Top with cut pieces of petals, golden popping candy and freeze-dried raspberries.
Tip: To use up the leftover marshmallow, dust a 20cm square shallow cake tin with 2 tablespoons of icing sugar and 2 tablespoons of cornflour. Pour the remaining marshmallow on top, then dust with another 2 tablespoons of icing sugar and 2 tablespoons of cornflour. Leave to set, then cut into squares and serve as sweets.