To make the macaroon shells, preheat the oven to 150C/300F/Gas 2 and line a baking tray with a sheet of silicone paper. Mark out rounds of 4cm/1.5in diameter on the reverse side of the paper with a pencil and set to one side.
Pulse the almonds with the icing sugar in a food processor and then pass through a sieve to get rid of any larger bits of almond. Put the egg whites with a pinch of salt in a free-standing food mixer with a whisk attachment and whisk until frothy, then gradually add the caster sugar a little a time, whisking in between each addition, until the whites are glossy and have firm peaks when the whisk is removed.
Towards the end of the whisking, add a few drops of food colour and then add the egg whites to the icing sugar and almonds. Mix until combined and so that the mixture falls off a spatula in ribbons. Put the mixture into a piping bag which has a small round nozzle attached, no bigger than 1cm/½in in diameter. Pipe the mixture onto the tray in the circles and leave to set for around 15 minutes.
Bake the macaroon shells for 12-15 minutes, until the shells peel off the paper easily. Leave them to cool on a wire rack.
For the lemon sponges, increase the oven temperature to 200C/180C (fan)/Gas 6. Grease the silicone moulds with melted butter, then dust with flour and set to one side.
Whisk together the egg with the sugar in a bowl until pale and frothy. Add the butter, flour, lemon zest and juice and baking powder and mix well until combined. Rest the batter for 20-30 minutes before pouring into the moulds and baking for 12-15 minutes.
Remove from the moulds and cool on a wire rack for 10 minutes. Dip each sponge into the limoncello and set to one side.
For the lemon sugar syrup, place the lemon juice and sugar in a small saucepan and bring to a boil for 4-5 minutes, or until thickened and syrupy. Remove from the heat and set to one side until cool.
To make the blueberry gel, place the blueberries into a food processor and blend to a purée. Sieve the purée into a saucepan to remove the skins and pips. Sprinkle the agar-agar flakes over the purée and place on the heat without stirring.
Once the mixture has heated through, stir and keep on the heat for 3-5 minutes. Pour into a cling film-lined cake tin and put into the fridge until set - around 30 minutes. Once set, break the jelly into pieces and put into the food processor with a few drops of lemon juice and blend until smooth and is a gel consistency. Transfer into a piping bag and keep cool until needed.
For the sherbet, mix together five teaspoons of the sugar, the citric acid and food colouring until the colour is even throughout. Taste to ensure that the sherbet is not too sour and add more sugar, to taste.
To assemble, brush a little of the lemon sugar syrup on the edges only of the sponges and then roll the edges in the sherbet. Scoop out a little hole in the top of the sponge, making sure not to go too deep and cut through the bottom of the sponge. Pipe a small blob of the blueberry gel in the hole. Place the whipped cream in another piping bag and pipe a small blob of cream on each sponge making sure to hide the hole and its contents.
Sandwich together the macaroons with the remaining gel and place a macaroon, on its side, on top of each sponge cake over the blob of whipped cream.