Ingredients:

  • 250g all-purpose flour
  • 400g granulated sugar
  • 65g Dutch-process cocoa powder
  • 2 tsp baking soda
  • 1 tsp baking powder
  • 1 tsp kosher salt
  • 240ml full-fat buttermilk, room temperature
  • 120ml vegetable oil
  • 2 large eggs, room temperature
  • 2 tsp pure vanilla extract
  • 240ml boiling water
  • 50g all-purpose flour (for filling)
  • 240ml whole milk
  • 200g granulated sugar (for filling)
  • 225g unsalted butter, softened
  • 1 tsp pure vanilla extract (for filling)
  • 1/4 tsp salt
  • 170g semi-sweet chocolate (60% cacao), finely chopped
  • 120ml heavy cream
  • 1 tbsp light corn syrup

Instructions:

  1. Preheat your oven to 350°F (175°C). Grease a 9x13-inch baking pan.
  2. Sift the flour, sugar, cocoa, baking soda, baking powder, and salt into a large bowl to ensure no lumps remain.
  3. In a separate vessel, whisk together the buttermilk, oil, eggs, and vanilla until well combined.
  4. Gradually incorporate the wet ingredients into the dry mixture using a whisk or hand mixer until smooth.
  5. Carefully whisk in the boiling water. The batter will be very thin; this ensures a moist crumb.
  6. Pour the batter into the prepared pan and bake for 30–35 minutes, or until a toothpick inserted in the center comes out with only a few moist crumbs. Cool completely.
  7. Prepare the Ermine filling by whisking 50g flour and 240ml milk in a small saucepan over medium heat until it thickens into a paste. Remove from heat and cool completely.
  8. Cream the butter and sugar for the filling until fluffy, then beat in the cooled flour paste and vanilla until it reaches a marshmallow-like consistency.
  9. Spread the filling over the cooled cake. Chill for at least 1 hour until the filling is firm to the touch.
  10. Prepare the ganache by heating heavy cream and corn syrup until simmering, then pour over chopped chocolate. Let sit for 5 minutes, whisk until smooth, and pour over the chilled cake.