1. Preheat oven to 350 degree F. Spray baking pan(s) with oil; set aside.
2. In a medium mixing bowl, cream butter and sugar until light and fluffy. Add eggs one at a time, beating well after each addition.
3. In a large mixing bowl, combine the flour, baking powder, and cream of tartar. In a small bowl, combine buttermilk and vanilla; add to the butter mixture and combine. Add butter mixture to the dry ingredients one third at a time, scraping the bowl frequently.
4. Bake until a toothpick inserted into the center comes out clean. Cool, then frost.
5. Perfect Frosting In a medium bowl, combine 1 cup unsalted butter at room temperature, 3 cups confectioners' sugar, 1 tablespoon vanilla extract, 2 tablespoons light corn syrup, and 1 tablespoon milk. For chocolate frosting, substitute 3/4 cup cocoa for 3/4 cup confectioners' sugar.