Preheat oven to 325F. Spray an 8-inch springform pan and line the bottom with parchment paper. Set on a baking sheet and set aside.
In a large bowl with an electric mixer or the bowl of a stand mixer with a paddle attachment, beat the butter with the brown sugar. Add the eggs one at a time, beating well after each addition. In a separate bowl, whisk together the hazelnut meal, flour, baking powder, salt, nutmeg. Add the dry mixture to the wet mixture and mix until combined. Fold in shredded apple.
Spoon batter in to prepared pan and level. Sprinkle with brown sugar and hazelnut meal for topping.
*Make sure you bake your cake with the cake pan on top of a baking sheet, to catch any moisture that may escape from the pan.
Bake cake in preheated oven for 60-80 minutes, or until golden, pulling away from the sides of the pan and a tester inserted in the centre comes out clean. Time will vary depending on the moisture in the apples you use.
Allow to cool in pan for 5 minutes, then run a knife around the outside and loosen and remove the outer ring. Allow to cool further, before cutting. Enjoy slightly warm or at room temperature with warm toffee sauce.
For the toffee sauce, combine the butter, brown sugar and cream in a microwaveable bowl. Heat on high for 30 seconds. Stir. Heat a further 15-20 seconds and stir again, until butter is melted. Microwave on high for 30-45 seconds more. Stir in vanilla. Serve warm over cake. Will keep in the fridge and can be re-heated as needed.
*You can also make this sauce in a small saucepan over medium heat. Heat, stirring, until melted. Allow to come to a boil, then boil for 30 seconds. Remove from heat and add vanilla.