Preheat and prepare pan. Preheat oven to 350°F (180°C). Grease and flour two 9-inch (23 cm) round cake pans (or you can use three 8" (20 cm) round cake pans). Set aside.
Combine dry ingredients. In a mixing bowl, whisk together cake flour, baking powder, and salt. Set aside. 3 ¼ cups (390 g) cake flour 1 teaspoon salt 1 tablespoon baking powder
Cream butter oil and sugar. In a second mixing bowl with an electric mixer on medium speed, cream butter, oil and sugar together until smooth and combined about 2 to 3 minutes. ½ cup (1 stick, 113 g) unsalted butter, ½ cup (120 mL) canola oil 2 cups (400 g) granulated white sugar
Add eggs, vanilla. Add the eggs one at a time, beating well after each addition. Scrape down the sides and bottom of the bowl after each addition. Add vanilla extract. Beat to combine. 4 large eggs 1 tablespoon vanilla extract
Alternate dry ingredients with buttermilk. Alternate adding the flour mixture with the buttermilk, beginning and ending with the flour mixture. Do not overmix. Stop mixing once the last of the flour has been mixed in. I like to give the last few stirs with a spatula to ensure it's not overmixed. 1 ½ cups (360 mL) buttermilk
Bake. Divide batter between your cake pans, smooth the tops. Bake for about 30-35 minutes The cake is done when it's golden brown on top and toothpick inserted into the center comes out clean or with a few moist crumbs. Remove cake from the oven and allow it to cool for 5 minutes, then turn it out onto a rack to cool completely.