Layers of nutty meringue, feather-light salted caramel buttercream and rich chocolate ganache make this a showstopping gluten-free cake. If you’re feeling brave, or just want to show off, try your hand at sugar work with the sugar dome to decorate.
Using the cake tin as a guide, draw a pencil circle on each of the pieces of paper lining the baking sheets. Return the pieces of paper to the baking sheets, pencil-side downwards.
Heat the oven to 190°C/170°C fan/375°F/Gas 5.
Make the meringues. Tip the icing sugar, chopped hazelnuts and ground almonds into a food processor. Blitz until the mixture resembles fine breadcrumbs.
Whisk the egg whites in the bowl of a stand mixer fitted with the whisk, on medium speed for 3–5 minutes, until the egg whites hold soft peaks.
Add the sugar, 1 tablespoon at a time, whisking well on medium speed between each addition until the mixture is smooth and the sugar is thoroughly incorporated. Continue whisking until you have added all the sugar and the meringue is bright white, silky smooth and very stiff (10–15 minutes). Using a large metal spoon, fold in the nut mixture taking care not to knock the air out of the meringue.
Using the spoon, divide the meringue mixture equally between the three baking sheets and spread it out into a disc to fill the circle template.
Bake the meringue discs for 25 minutes, until lightly golden. Remove them from the oven and set the meringue discs on a wire rack. Leave until cold, then carefully peel off the baking paper.
Meanwhile, prepare the salted caramel. Heat the sugar with 3 tablespoons of water in a heavy-based saucepan over a low heat, gently swirling the pan from time to time (but don’t stir), until the sugar dissolves.
Increase the heat, bring the syrup to the boil and continue to cook, without stirring, until it turns an amber colour, then take the pan off the heat.
Carefully pour in the cream and sea-salt flakes in a steady stream, whisking continuously. If the caramel begins to harden, return to the heat and whisk until completely smooth. Leave to cool completely.
Make the chocolate ganache. Tip both chocolates into a heatproof bowl. Pour the cream into a medium saucepan and place over a medium heat. Bring to the boil, then immediately remove the pan from the heat and pour the cream over the chocolate. Leave for 2 minutes, until smooth. Set aside.
Make the Italian meringue buttercream. Place the sugar and 3 tablespoons water in a small saucepan set over a low heat. Once the sugar has dissolved, increase the heat to a rapid boil until the syrup reaches 121°C on the sugar thermometer.
Meanwhile, whisk the egg whites in the bowl of a stand mixer fitted with the whisk, on medium speed until the egg whites hold soft peaks.
Remove the syrup from the heat and, with the whisk at full speed, slowly pour the hot syrup onto the egg whites in a thin stream. Continue whisking until the meringue is very thick and glossy and the bowl is cool to the touch.
Gradually add the butter, whisking after each addition until the buttercream is smooth and thick.
Tip the cooled caramel into the meringue buttercream, and whisk until fully incorporated. Chill the butter cream until you’re ready to use it.
Make the honeycomb. Put the sugar and golden syrup into a deep, medium pan and set it over a low heat. Once the sugar and syrup have dissolved, increase the heat to a rapid boil until the syrup reaches 150°C on the thermometer.
Tip in the bicarbonate of soda and gently whisk to incorporate. Quickly pour the bubbling honeycomb mixture into the lined baking tin. Leave it to set completely (only a few minutes), then break it into shards.
To assemble the dacquoise, set one of the meringue layers on a large, flat serving plate and spread it with a third of the meringue buttercream. Place another meringue layer on top and spread with the chocolate ganache. Top with the last meringue layer. Reserve ¼ of the remaining buttercream and then spread the rest of it over the top and sides. Spoon the reserved buttercream into the piping bag fitted with a star nozzle and pipe swirls of meringue buttercream around the top edge of the dacquoise.
Press the toasted flaked almonds onto the sides of the dacquoise and place it in the fridge to chill.
Make the sugar dome, if using. Place the sugar, glucose and 3 tablespoons of water in a small saucepan set over a low heat. Once the sugar has dissolved, increase the heat to a rapid boil until the syrup reaches 145°C on the thermometer. Cool the sugar until the temperature decreases to 115°C.
Set the cake ring on top of the cling film surface over the bowl and carefully pour the syrup into the centre of the ring. Place gentle pressure with your fingertips around the outside of the cake ring, encouraging the sugar dome to slowly rise upwards. Keep even pressure for 5–10 minutes, while the dome sets. Carefully remove the cake ring from the base of the sugar dome.
Place shards of honeycomb around the edge of the dacquoise, to form a ring with the piped buttercream and arrange some honeycomb in the middle. If you have made the sugar dome, place it in the middle of the dacquoise. Serve immediately.