Preheat the oven to 350°F. Either butter or spray using non-stick baking spray a 9" x 13" baking pan. Set aside.
In a medium-size mixing bowl, stir together the flour, baking powder and salt.
In a large mixing bowl, cream butter, oil, and sugar until well combined, about 3-4 minutes. Note 3
Add eggs, one at a time, beating after each addition to blend each egg into the batter
Then, stir in vanilla extract.
Gently fold half of the flour mixture into the wet ingredients, then add the milk, then add remaining flour mixture.
Pour batter into prepared baking pan. Bake for 35-40 minutes, until an inserted toothpick comes out clean.
Once cake is cool, use a skewer to poke holes all over the cake.