1. Line two baking trays with non-stick parchment paper. Place the ground almonds, pistachios and icing sugar into a food processor and blend for 15 seconds. Sieve the mixture into a large bowl.
2. Separate the egg whites and discard the yolks. Pour the egg whites into a large, grease-free mixing bowl. Whisk until it forms soft peaks.
3. Gradually add in the caster sugar, one tablespoon at a time. Whisk until it forms stiff peaks. The meringue should be firm and glossy. Whisk in the vanilla.
4. Using a spatula, fold in the pistachio mixture, one-third at a time. When all the dry mix is thoroughly incorporated, continue to cut and fold the mix until it forms a shiny batter with a thick, ribbon-like consistency. Fold in 1-2 drops green food colouring.
5. Pour the mix into a piping bag with a 1cm round nozzle. Pipe 32 rounds onto the prepared tray.
6. Sprinkle on some finely chopped pistachios onto each. Tap the tray onto the counter to remove any air bubbles. Leave to sit at room temperature for 30 minutes.
7. Preheat the oven to 160 ̊C/140 ̊C fan/gas mark 3.
8. Bake in the prepared oven for 10-15 minutes. Leave to cool for 10 minutes and then carefully peel the macarons off the baking paper. Leave to cool fully.
9. In a large bowl, beat together all of the ingredients for the buttercream until smooth. If the mix is too thick, add 1-2 tablespoons of boiling water to loosen the icing.
10. Spoon the mix into a piping bag, snip a small hole in the end of the bag. Pipe a swirl of buttercream onto one of the macarons and sandwich together with another. Repeat until all are sandwiched.

Per Serving: 135kcals, 6.1g fat (2.3g saturated), 19.3g carbs (18.2g sugars), 1.9g protein, 0.6g fibre, 0.41g sodium