Start by preheating your oven to 350°F (175°C). Grease an 8-inch (20 cm) round cake ring or springform pan thoroughly and line the bottom with baking paper.
If using a cake ring, place a layer of aluminum foil underneath and add baking paper on top, making sure the base is well sealed from the outside. This helps the cake release easily after baking while keeping its edges perfectly straight and neat.
In a medium bowl, combine the milk with vinegar (or lemon juice) and yogurt. Let the mixture rest for about 5 minutes. During this time, the milk will curdle slightly, creating a natural buttermilk substitute that adds tenderness and a subtle tang to your cake.
Next, add the sugar, oil, and vanilla extract to the curdled milk. Whisk gently until the sugars dissolve and the mixture becomes smooth and uniform.
Meanwhile, in a separate bowl, sift together the all-purpose flour, cocoa powder, 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.
Pour the batter into the pan, smoothing the tops with a spatula. Bake in the preheated oven for 25 minutes, or until a toothpick inserted into the center comes out clean and the surface springs back when gently pressed. Once baked, allow the cake to cool in the pan to set.