Viennese biscuits

Name: Viennese biscuits
Prep time: 15 min
Cook time: 12 min
Total time: 27 min
Cuisine: European
Ingredients: 125 g butter (room temperature); 100 g icing sugar (US powdered sugar); 5 medium egg yolks (room temperature); ½ tsp pure vanilla extract or 1/4 tsp of vanilla paste; 1 pinch fine sea salt; 1 whole orange (zested); 200 g plain flour (all-purpose); 30 g cornflour (2 tablespoons); 80 g dark or milk chocolate (chopped); 3 tbsp whole roasted pistachios (crushed)