In a bowl cream together the butter and the sugar.
Add the egg, salt and vanilla and mix well.
Add the flour and baking powder.
Finally work the walnuts and the apples into your dough.
Chill for 20min in the fridge and heat your oven to 180°C / 356°F.
Roll the cookie dough into little balls and place on a baking sheet. Leave some room, because the dough will spread. Bake for 10-15 min or until golden brown.