First, prepare the vegan buttermilk by combining soy milk with apple cider vinegar in a bowl. Stir it lightly and leave it aside for about 5 minutes so it can curdle and become slightly thick.
Next, make the ganache filling. Warm the plant milk gently, then pour it over the chopped chocolate. Add vegan butter and mix everything together until it becomes smooth and glossy. Keep it aside so it can thicken.
Now preheat your oven to 200°C (392°F) and lightly grease two ramekins with a little vegan butter so the cakes don’t stick.
In a separate bowl, combine the dry ingredients: flour, cocoa powder, baking powder, salt, sugar, and instant coffee. Mix them well so everything is evenly distributed.
Pour in the melted vegan butter, vanilla extract, and the prepared vegan buttermilk into the dry mixture. Stir slowly and gently until it turns into a smooth cake batter without lumps.
Divide the batter equally into the prepared ramekins, filling them about halfway. Place 1 to 2 tablespoons of the prepared ganache right in the center of each ramekin.
Cover the ganache with the remaining batter, making sure it is fully sealed inside, and lightly smooth the tops.
Bake in the preheated oven for 10 to 12 minutes. The edges should look set while the center stays soft and slightly jiggly.
Once baked, let them rest for about 2 minutes. Then carefully turn them out or serve straight in the ramekins while still warm so the chocolate center flows out when cut.