Mocha and hazelnut meringue pie

Ingredients

• 300 gram egg whites
• 530 gram sugar
• 200 gram hazelnuts
• 500 ml milk
• 3 packages of vanilla sugar or use vanilla extract
• 4 egg yolks
• 2 tablespoons all-purpose flour
• 100 ml espresso (or strong coffee)
• 500 gram butter (room temperature)
• 100 gram powdered sugar
• large handful of nougatine nuts
• optional: cocoa powder for garnish
• few drops of lemon juice