Preheat the oven to 190°C (fan oven 170°C), gas mark 5. Line 2-3 baking sheets with non-stick baking parchment and set aside.
Put the ground almonds and icing sugar together in the bowl of a food processor or blender and whizz together for about 5 secs.
Put the egg whites and dried egg white powder into a large, clean bowl and whisk together until they form stiff peaks. Gradually whisk in the caster sugar until the mixture is very thick and shiny.
With a large metal spoon, quickly fold the almond and icing sugar into the meringue until evenly blended.
Spoon the mixture into a piping bag fitted with a 1cm (1/2in) nozzle. Pipe rounds about 3.5cm (1.5in) in diameter onto the lined baking sheets, leaving the same amount of space between each one. You should get at least 30 rounds. Set them aside for 15 mins to allow the macaroons to form a crust on top.
Bake in the preheated oven for about 5 mins or until the base has set. Then, using a palette knife, gently ease the macaroons off the paper and flip them over to bake the underside. Bake for a further 5 mins, then leave to cool on a wire rack.
Meanwhile, make the filling. Beat together the confiture de caramel and peanut butter. Sandwich the macaroons with the caramel mixture, spreading it right to the edge of the rounds. Finally, roll the filled macaroons in chopped pistachio nuts. Eat within 2 hrs.
If you don't like peanut butter, beat enough confiture de caramel into 75g (3oz) mascarpone cheese to form a smooth, spreadable consistency. Sandwich the macaroons and roll them in toasted desiccated coconut.
Instead of piping mixture, it is possible to drop even spoonfuls into rough rounds on the baking sheets. They won't have the dainty look of piped ones but will taste just as good and have a charm of their own!