With the rack in the middle position, preheat the oven to 250°F (120°C). Butter an 8-inch (20 cm) square baking pan and line with parchment paper, letting it hang over two sides.
In a small food processor, finely chop the almonds and pistachios with the cornstarch.
In a bowl, whisk the egg white and cream of tartar with an electric mixer until foamy. Gradually add the sugar, while whisking, until stiff peaks form. Fold in the nut mixture with a spatula or whisk. Spread evenly in the baking pan.
Bake for 35 minutes. Let cool completely in the pan. Pass a thin blade between the pan and the dacquoise. Unmould and break into pieces.
Meanwhile, place the chocolate and cardamom in a bowl.
In a small pot, bring the cream to a boil. Pour over the chocolate and let sit for 1 minute without stirring. Whisk the mixture until smooth. Cover and refrigerate for 2 hours. The ganache will keep for 1 week in an airtight container in the refrigerator.
In a separate small pot, bring the orange juice and sugar to a boil. Let reduce by half. The syrup will keep for 1 week in an airtight container in the refrigerator.
On a work surface, supreme the oranges by removing the skin, pith and membrane with a knife and divide into skinless sections.
On each plate, place a quenelle of ganache, about 3 tbsp (45 ml) in size. Add a few segments of orange and a few pieces of dacquoise. Drizzle with orange syrup. Sprinkle with chopped pistachios, if desired.
Recipes with the "Healthy Pick" stamp have been evaluated by a registered dietitian member of the Ordre professionnel des diététistes du Québec.