1 Preheat the oven to 180°C(160° fan)|350F|gas 4. Grease and line two large baking trays with greaseproof paper.
2 Combine 450 g of icing sugar with the ground almonds in a large mixing bowl.
3 Beat the egg whites with a pinch of salt in a separate, clean mixing bowl until stiffly peaked. Fold the egg whites into the ground almond mixture and then divide between four small bowls.
4 Colour the mixtures with the assorted food dyes, mixing thoroughly until uniformly coloured.
5 Spoon the macaroon mixture into separate piping bags fitted with round nozzles. Pipe 12 rounds of each mixture onto the baking trays, spaced apart.
6 Leave them to set for 15 minutes, and then bake for 8–10 minutes until just set.
7 Remove to a wire rack to cool. Heat the cream in a heatproof bowl in the microwave until hot, then add the chocolate and stir until smooth.
8 Beat together the butter and icing sugar in a mixing bowl using an electric mixer. Once pale and thick, divide the mixture between two bowls.
9 Blitz the pistachios in a food processor until finely ground, and then add to one bowl, stirring well to incorporate. Spoon the four fillings into separate piping bags.
10 Pipe the buttercreams and jam onto the underside of the macaroons, sandwiching them against the other macaroon halves to complete.