Preheat oven to 350°F (175°C). Prepare two 6-inch (15 cm) round cake pans by greasing them thoroughly and lining the bottoms with baking paper. This ensures your cakes release easily after baking and maintain their perfect shape.
In a medium bowl, combine room temp milk, vinegar (or lemon juice) and plain yogurt and let the mixture rest for about 5 minutes. During this time, the milk will curdle slightly, creating a natural buttermilk substitute
Add sugar, oil, and vanilla extract to the curdled milk. Whisk gently until the sugar dissolve and the mixture becomes smooth.
In a separate bowl, sift together the all-purpose flour, cocoa powder, instant coffee, baking soda, baking powder, and salt to evenly distribute the dry ingredients and prevent lumps.
Slowly incorporate the dry mixture into the wet ingredients, whisking until you achieve a smooth, lump-free batter.
Divide the batter evenly between the prepared pans, smoothing the tops with a spatula.
Bake in the preheated oven for 25 to 30 minutes, or until a toothpick inserted into the center comes out clean and the surface springs back when gently pressed.
Allow the cakes to cool in their pans for 30 minutes to set, then carefully transfer them to a wire rack to cool completely. Trim a thin layer of the cake before assembling.