Pour 1 cup of milk into a bowl.
Add 1 tablespoon of white vinegar or apple cider vinegar to the milk and gently stir the mixture with a spoon. Ensure that the vinegar is well distributed throughout the milk.
Allow the mixture to sit at room temperature for about 5 to 10 minutes. During this time, the acid in the vinegar will react with the proteins in the milk, causing it to thicken and curdle slightly.
After 5 to 10 minutes, check the consistency. The milk should appear slightly thicker and may have small curdles.
If you already have store-bought buttermilk or prepared buttermilk at home, you can certainly skip the above steps of making it from scratch.
Preheat your oven to 180°C. Line a muffin tin with cupcake liners.
In a large mixing bowl, whisk together the flour, baking powder, cocoa powder, baking soda, and salt until well combined and sift it.
In a separate bowl, whisk the buttermilk, sugar, oil and vanilla extract. Whisk well until the sugar is dissolved.
Add the dry ingredients to the wet ingredients in two batches and stir until just combined and there are no lumps. Be careful not to overmix.
In a cup, mix the instant coffee powder with hot water and stir until fully dissolved. Add this to the batter and combine gently with a whisk or a spatula.
Divide the batter evenly among the cupcake liners, filling each about two-thirds full.
Bake in the preheated oven for 15-20 minutes or until a toothpick inserted into the centre comes out clean.
Allow the cupcakes to cool in the tin for a few minutes before transferring them to a wire rack to cool completely.