Sift the almond powder, icing sugar, cornstarch, cocoa powder, and salt into a large bowl to remove lumps and ensure even mixing.
Add the cream and egg whites to the dry mixture. Whisk until the batter is smooth, ensuring all ingredients are well integrated.
Fold in the melted dark chocolate gently for a rich, cohesive batter. Refrigerate overnight for the best texture and flavor development.
Preheat the oven to 150°C. Pour the batter into silicone molds, ensuring they are filled evenly. Use a spatula to smooth the tops for a clean finish.
Bake the financiers for 12–15 minutes or until set and firm to the touch. Let them cool briefly before transferring them to the freezer for easy removal. Once the financiers are fully set, use a narrow piping nozzle to pierce a small hole in each center for your chosen filling.
Place the roasted almonds and hazelnuts in a food processor. Blend until a smooth, creamy paste forms, ensuring the nuts' oils are released.
Add the icing sugar to the nut paste and continue blending until fully combined and smooth.
Gradually pour the melted milk chocolate into the food processor. Blend until the mixture becomes silky and homogenous.
Carefully remove the financiers from their molds. Use a piping bag with a narrow nozzle to fill the center hole of each financier with creamy gianduja. Pipe a decorative swirl of the whipped ganache on top of each financier, creating an elegant and professional look.
For an extra touch of sophistication, garnish the financiers with a sprinkle of cocoa powder, edible gold leaf, or crushed nuts.