Instructions:
- Preheat oven to 350°F (175°C). Grease and flour a 9x13 inch baking pan.
- Whisk dry ingredients (flour, sugar, cocoa, baking soda, salt) in a large bowl.
- In a separate bowl, whisk together wet ingredients (oil, buttermilk, eggs, vanilla, food colouring).
- Gradually add the wet mixture to the dry mixture; mix until just combined, being careful not to overmix.
- Mix the vinegar into the hot coffee/water, then quickly stir this into the batter. The batter will be thin.
- Pour batter into the prepared pan and bake for 30–35 minutes, or until a skewer inserted near the centre comes out clean. Let the cake cool in the pan for 15 minutes.
- While the cake cools slightly, prepare the soak: Whisk the 4 oz of softened cream cheese into the can of condensed milk until mostly smooth.
- Using the end of a wooden dowel or thick chopstick, poke holes all over the warm cake, spaced about ¾ inch apart, going nearly to the bottom of the pan.
- Slowly and evenly drizzle the condensed milk mixture over the entire surface of the cake, allowing it to pool and sink into the holes.
- Cover the cake loosely and refrigerate for a minimum of 3 hours, or overnight for maximum moisture infusion.
- Prepare the frosting: Beat the softened butter and 8 oz cream cheese together until light and fluffy. Gradually add the sifted powdered sugar, vanilla, and salt. Beat until smooth and spreadable.
- Once the cake is thoroughly chilled, spread the cream cheese frosting evenly over the top. Slice and serve cold.