Hazelnut Vanilla Layer Cake {Esterhazy Schnitten}

Ingredients

• 2½ tsp tapioca flour
• 1 vanilla bean, split lengthwise, seeds scraped out, pod and seeds reserved
• 2½ tbsp powdered sugar
• 5 large egg whites, room temperature
• ¼ cup + 2 tbsp sugar
• 5 large egg yolks
• 1 tsp ground espresso
• pinch of cream of tartar
• ½ cup sugar
• ¼ cup sliced almonds, lightly toasted and cooled
• ½ lb unsalted butter, slightly soft but still cool
• 1¼ cups hazelnuts, toasted and cooled
• ½ cup half and half
• ½ tsp kosher salt
• scant ¼ tsp kosher salt