Frankfurt Crown Cake

Ingredients

• For the sponge cake
• 7 ounces butter, at room temperature | 200g
• 8 ounces sugar | 225g
• a pinch fresh vanilla
• 6 eggs
• 7 ounces plain flour, sieved | 200g
• 3.5 ounces cornstarch | 100g
• 3 teaspoons baking powder
• a pinch salt
• breadcrumbs to sprinkle the bundt pan
• For the buttercream and caramelized hazelnuts
• 9 ounces butter, at room temperature | 250g
• 4 egg yolks, at room temperature
• 2 ounces cornstarch | 60g
• 4.5 ounces sugar | 120g
• 17 ounces milk, at room temperature | 500ml
• 1 vanilla bean, slit slightly
• a pinch salt
• 7 ounces hazelnuts, finely chopped | 200g
• 3.5 ounces sugar (for the caramelized hazelnuts) | 100g
• 1.5 ounces butter (for the caramelized hazelnuts) | 35g