Preheat your oven to 325 degrees F.
In a medium sized mixing bowl, whisk together the flour, baking powder, and salt. Set aside.
In a mixer fitted with the paddle attachment, beat the sugar and butter for about 2 minutes. Add the oil and beat for another 2 minutes, until light and fluffy.
Add the eggs and egg whites, one at a time, and mix well after each addition. Add the vanilla and strawberry extract or emulsion.
With the mixer on low, alternatively add the flour mixture with the strawberry puree and buttermilk, starting and finishing with the flour mixture. Mix until just incorporated.
Evenly divide the batter between the three pans, about 17 ounces in each.
Bake the cake layers for about 33 to 38 minutes, until a toothpick inserted in the center comes out with just a few moist crumbs on it.