Combine the 'fed' starter, milk and flour in a large mixing bowl. Cover and rest at room temperature for 2~3 hours. It will be slightly bubble and expand just a little bit.
Preheat the oven to 350°F. Lightly grease a 9"x13" baking pan.
In a separate bowl, beat together the sugar, oil, salt, baking soda, cocoa, espresso powder and vanilla extract.
Add eggs, one at a time (or the egg replacer mixture) and beat well until combined.
Gently add the chocolate mixture into the starter-flour-milk mixture and stir until smooth. It will be a little gloppy at first but will smooth out eventually.
Pour the batter into the prepared pan.
Bake the cake for 30~40 minutes or until a cake tester inserted into the center comes out clean.
Remove the cake from the oven and set it on a wire rack to cool.