Ingredients:

  • 312 g all-purpose flour (2½ cups)
  • 300 g granulated sugar (1½ cups)
  • 5 g baking soda (1 teaspoon)
  • 6 g fine salt (1 teaspoon)
  • 1 g unsweetened cocoa powder (½ teaspoon)
  • 240 ml vegetable oil (1 cup)
  • 240 ml buttermilk, room temperature (1 cup)
  • 100 g large eggs, room temperature (2 eggs)
  • 10 ml pure vanilla extract (2 teaspoons)
  • 15 ml white vinegar (1 tablespoon)
  • 15 ml purple gel food coloring (1 tablespoon)
  • 225 g unsalted butter, softened (1 cup)
  • 480 g powdered sugar (4 cups)
  • 10 ml pure vanilla extract (2 teaspoons), for the frosting
  • 30 to 45 ml heavy cream (2 to 3 tablespoons)
  • Pinch of fine salt

Instructions:

  1. Heat the oven to 180°C (350°F). Grease two 9-inch round cake pans and line each bottom with parchment.
  2. Set the buttermilk and eggs out at room temperature for 30 minutes. For a quick shortcut, place the eggs in a bowl of warm water for 5 minutes.
  3. In a small bowl, whisk the buttermilk with the vinegar. Let it sit for 2 minutes until slightly thickened and curdled.
  4. In a large bowl, whisk together the flour, sugar, baking soda, salt and cocoa powder until no lumps remain.
  5. In a medium bowl, whisk the oil, eggs, vanilla and purple gel coloring until the color is uniform and glossy.
  6. Pour the wet mixture into the dry bowl, then add the buttermilk mixture. Stir gently until just combined. A few small streaks are fine.
  7. Stop mixing as soon as the batter is smooth and even violet with no white flour patches.
  8. Divide the batter evenly between the two pans and smooth the tops with a spatula.
  9. Bake for 28 to 32 minutes until the tops spring back when lightly pressed, the edges pull away from the pan, and a toothpick comes out with a few moist crumbs.
  10. Cool the layers in their pans for 10 minutes, then turn them out onto a wire rack. Cool for about 50 minutes until fully cool.
  11. If the layers are domed, level them with a serrated knife once fully cool.
  12. Beat the softened butter on medium speed for 2 minutes until creamy.
  13. Add the powdered sugar, pinch of salt and vanilla on low speed, then beat for 3 minutes until fluffy.
  14. Add 2 tablespoons of heavy cream and beat on medium. Add more cream one spoonful at a time until the frosting is spreadable but still holds soft peaks.
  15. If the frosting feels soft, refrigerate it for 30 minutes before spreading.
  16. Place one cake layer on a serving plate and spread a thin layer of frosting over it. Top with the second layer.
  17. Spread a thin crumb coat of frosting over the top and sides. Refrigerate for 15 minutes.
  18. Spread the remaining frosting over the top and sides of the cake. Slice into 14 slices to serve.