Preheat oven to 350 degrees F.
Grease 9x5 loaf pan,
Beat butter and sugar until fluffy.
Add buttermilk and baking powder, combining.
Add eggs and vanilla.
Add flour and salt.
Stir in apple.
Pour batter into pan and smooth top with offset spatula.
Sprinkle on Streusel and bake 60 minutes.