This entremet has four layers, each with a distinct flavour: an orange-blossom almond sponge, a set lemon curd, a caramelised honey set custard, and finally a gelée topping made with puréed blackberries.
Heat the oven to 180°C/160°C fan/350°F/Gas 4. Melt the butter in a small pan and leave to bubble gently over a medium–low heat, until it turns a nut-brown colour. Set aside to cool to room temperature.
Sift half the sugar, all the ground almonds, and the flour into a bowl. In a separate bowl, whisk the egg whites, with the salt, until they form soft peaks. Whisk in the remaining sugar, a little at a time, until the meringue stands in stiff peaks.
Sprinkle the flour mixture and the grated lemon and orange zests on top and start to fold in by hand. When the flour is half-combined, trickle in the melted butter, the orange blossom water and the vanilla bean paste, and fold again to fully combine.
Spoon the mixture into the cake tin and bake for 20–25 minutes, until golden brown. Transfer to a wire rack, unmould the cake from the tin and leave to cool.
Clean the cake tin and press the card base into the bottom. Cut a wide strip of acetate to fit inside the rim, like a collar, and secure with tape. Remove the paper from the sponge, turn the sponge top downwards and place on the card base, pressing it down firmly. Tighten the acetate to fit, if necessary.
To make the lemon set curd, pour the lemon juice into a medium pan, sprinkle over the agar-agar, and place the pan over a medium–low heat. Bring to the boil without stirring, then simmer for 8 minutes, to dissolve the flakes.
Meanwhile, break the eggs into a heatproof bowl, add the sugar and whisk for 2–3 minutes, until smooth, then whisk in the lemon mixture. Return to the pan and stir over a medium–low heat, just until it thickens to coat the back of a spoon. Remove from the heat.
Stir in the butter, a little at a time, then strain the curd into a bowl. Leave to cool to room temperature, stirring as it thickens. Spoon the curd on top of the sponge and chill for 4–5 hours, until set.
Make the honey set custard. Soften the gelatine in water. Put the honey into a medium pan, add the vanilla paste and set over a medium–low heat. Simmer, stirring occasionally, until the honey thickens and darkens. Remove from the heat and hand whisk in the cream and milk. Return to the heat and whisk until smooth and hot. Remove from the heat.
Put the egg yolks into a heatproof bowl, add the salt and sugar, and whisk for 2–3 minutes, until smooth.
Whisk in the hot honey cream, then pour the mixture back into the pan. Return to a medium–low heat and stir until the custard thickens to coat the back of the spoon. Remove the pan from the heat.
Lift the gelatine out of the water, squeeze out the excess water, and stir into the hot custard to dissolve. Strain the custard into a jug. Leave to cool and thicken, stirring frequently, then pour on top of the lemon curd. Chill to set.
To make the gelée, soak the gelatine as before. Put the blackberries and lemon juice into a medium pan over a medium heat. Stir as the berries release their juice and the mixture comes to a boil, then simmer, stirring frequently, for about 10 minutes, until the berries are very soft. Remove from the heat and mash to a thick purée, then add the butter and sugar and stir until melted.
Beat the eggs in a heatproof bowl, then whisk in the hot blackberry purée. Return to the pan and stir over a low heat until thick but not boiling.
Remove from the heat, then stir in the gelatine to dissolve as before, then strain the blackberry mixture into a jug. Cool to room temperature, stirring frequently. When the gelée starts to thicken, pour it over the top of the custard, then chill to set.
To serve, carefully remove the entremet from the tin, peel away the acetate and serve decorated with blackberries and dusted with icing sugar.