Cream together butter, oil and sugar until soft and creamy

Add eggs one at a time, beating well after each addition

Add vanilla

In a separate bowl mix flour, baking powder and salt

Using a spatula and gently hand-mixing, alternate adding flour mixture and buttermilk to the butter mixture, starting and ending with flour mixture and mixing until just combined after each addition.  The batter should be smooth and completely combined, but avoid over-mixing.

Put in a baking pan and bake for 30-35 min