Preheat oven to 350° (325° for dark pans)
Use a baking spray to prepare 2-13X9 baking pans then place parchment on the bottom of each pan and give the parchment a light spray to ensure the cakes will release easily after being baked.
In a large mixer bowl beat sugar and eggs.
Mix in flour, baking powder, milk, butter, oil, and vanilla.
Mix until smooth and completely blended.
Pour batter evenly into each pan and bake for 35-40 minutes or until a toothpick comes out fairly clean, do not overbake. Check the cake every minute if needed to be sure you don't overbake it.
Allow the cakes to cool until cool, about 30 minutes, then release them from the cake pans onto cooling racks until the cakes are completely cooled.
I typically bake large cakes like this a couple of days ahead of when they are needed, so I can freeze the cake to make it easier to frost and they stay moist and stay together nicely without crumbling and falling apart when sliced.
I wrap my cakes at this point with plastic wrap and put them in the freezer. I put them on cardboard to keep them flat so they hold their shape.
Freeze the cakes until firm (a couple of hours at minimum to a few days- if you will be freezing them for more than a few days be sure to wrap them extra well so there is no frost on the cakes when you go to take them out of the freezer).
Unwrap the cakes and allow them the cakes to be at room temperature for 20 minutes to be able to handle them and stack them with filling. They won't bend much, so level cakes are best. I don't prefer to trim my cakes so I place the tops of each cake in the center and add the filling to adjust for any unevenness.
*I prepare the filling the day ahead so it's really cold and will fill in the middle of the cakes nicely.
I like to prepare the frosting the day I'm using it.