Cook stirring for about 5 minutes. Let the apples simmer until most of the juice has evaporated, about 15 minutes until they start to brown. Remove from heat and let cool.
Place the all-purpose flour, hazelnut flour, brown sugar, and salt in a bowl. Whisk to combine.
Beat the egg with a fork or whisk in a small separate bowl and add to the streusel mix. Add the butter and use a fork or your hands to knead everything together to form a streusel.
Layer in the apple whiskey honey mixture evenly spreading it into the shell. Distribute the rest of the streusel evenly over the apples. Sprinkle the remaining tablespoon of whiskey over the top.
Remove from oven. When the cake is cool enough to serve (15-20 minutes). Remove the cake from the pan, transfer to a cake plate.
Drizzle the remaining tablespoon of home over the top and sprinkle with the chopped hazelnuts. Cut and serve.