Preheat the oven to 160° C fan.
Distribute some butter all over the baking tin - only inside! Add some flour & shake well. The inside of the baking tin should be covered completely - thinly.
Clean, peel & trim the apples; chop into small bits.
Mix butter, sugar, vanilla sugar, salt & eggs w/ the handheld electric mixer.
Mix flour, baking powder & spice mix.
Combine everything.
Add the apple bits.
Pour the mess into the baking tin.
Bake in the preheated oven for about 45 min. Make the famous test w/ the wooden pin - if necessary add another 5 min.
Let the cake cool down for about 15-20 min in the baking tin; then let the cake tumble out.
When at room temperature mix icing sugar & lemon juice until thick enough for the icing you prefer. Distribute on top of the cake & sprinkle w/ chopped pistacchios.