Ingredients:

  • 313 g all-purpose flour
  • 300 g granulated sugar
  • 6 g fine salt
  • 5 g baking soda
  • 180 ml vegetable oil
  • 150 g large eggs (3), room temperature
  • 240 ml buttermilk, room temperature
  • 15 ml white vinegar
  • 10 ml vanilla extract
  • 15–30 ml purple gel food coloring
  • 225 g cream cheese, softened
  • 113 g unsalted butter, softened
  • 420 g powdered sugar, sifted
  • 5 ml vanilla extract
  • pinch of fine salt
  • 15 ml heavy cream, optional

Instructions:

  1. Preheat the oven to 180°C (350°F). Grease two 23 cm (9-inch) round pans, line the bottoms with parchment, and grease the parchment.
  2. Microwave the cream cheese in 10-second bursts until it gives slightly under pressure but still holds its shape. Repeat with the butter if it is firm.
  3. In a medium bowl, whisk together the flour, salt, and baking soda.
  4. In a large bowl, whisk the sugar, vegetable oil, and eggs one at a time until smooth. Add the vanilla and purple gel coloring, then whisk for about 1 minute until glossy and uniform. Add enough gel coloring to reach a clear violet.
  5. Stir the white vinegar into the buttermilk. The mixture will look slightly curdled.
  6. Add one-third of the flour mixture to the wet ingredients and mix on low until barely combined. Add half the buttermilk mixture, then another third of the flour, the rest of the buttermilk, and finally the last of the flour. Stop mixing as soon as no white streaks remain.
  7. Divide the batter evenly between the two pans. Use a kitchen scale if you have one.
  8. Bake for 28–32 minutes, rotating the pans halfway through, until the edges pull slightly away from the pan, the top springs back when touched lightly, and a toothpick inserted in the center comes out with a few moist crumbs, not wet batter.
  9. Cool the cakes in their pans for 10 minutes, then invert them onto a wire rack and cool completely, about 1 hour.
  10. Optional: freeze the cooled layers for 15 minutes before frosting so they are firmer and easier to stack.
  11. Beat the cream cheese and butter on medium for about 2 minutes until smooth. Add the powdered sugar gradually, then the 5 ml vanilla extract and the pinch of salt. Beat for 2–3 minutes until fluffy. If the frosting is too stiff, add the heavy cream 1 tablespoon at a time.
  12. Level the cake tops if needed. Place one layer on a plate and spread a thin layer of frosting over it. Add the second layer, then apply a thin crumb coat over the whole cake and refrigerate for 10 minutes.
  13. Finish with a thicker layer of frosting over the chilled cake. Cut into 12 slices and serve.