Preheat your oven to 350°F. Line 2 or 3 large baking sheets with parchment paper, and set aside.
In a medium bowl, combine flour, baking powder, and salt. Whisk to incorporate, and set aside.
In a separate large bowl, cream together your sugar, butter, and oil until it's relatively smooth (some graininess is fine).
Add your eggs to the sugar mixture, one at a time, whisking well after each addition. Add your sour cream and vanilla extract, and whisk to combine.
Combine the dry ingredients and wet ingredients. Mix everything together until you no longer see any dry spots of flour. Take care not to over mix - some lumps are fine!
Fill some of your batter into a large piping bag or plastic bag. Pipe 3 rounds of batter onto your parchment lined baking sheets, each about 9 inches large. Smoothen the tops to fill in any gaps and even out the tops. The cakes will expand as they bake, so make sure they have plenty of space if you plan on baking more than one round on the same baking sheet. If needed, you can bake 2 to 3 batches. The batter can sit out for up to 30 minutes at room temperature.
Bake in the center of your preheated 350°F oven for 10 to 15 minutes, or until the edges turn lightly golden brown and a skewer inserted into the center of the cake comes out clean.
Cool for 5 minutes on the baking sheet, then transfer the cakes (still on the parchment paper) onto a wire rack to cool completely to room temperature. Before frosting, stick the cakes into your freezer for about 20 or 30 minutes to firm up. It'll make them easier to take off the parchment paper and easier to handle! Frost with your favorite frosting (I used vanilla buttercream)!