Preheat oven to 350 degrees F. Grease & flour a 9×13 inch pan.
Combine milk & lemon juice and set aside. (The mixture will thicken slightly)
Combine flour, sugar, cocoa, baking soda & baking powder in a large bowl.
Add eggs, coffee, soured milk, oil and vanilla. Beat medium speed for 2 minutes. Pour into prepared pans. (Your batter may seem runny at this point but it will bake up beautifully.)
Bake 30 to 40 minutes, or until toothpick inserted into center of cake comes out clean. Be sure to check the cake at 30 minutes so it doesn’t over cook.
In a saucepan, combine sugar, cocoa powder, cornstarch and salt, mix well. Add in cold milk, stir until combined.
Turn heat to medium high stirring constantly until mixture comes to a boil.
Allow to boil for 1 minute while stirring, remove from heat and stir in butter.
Allow to cool for 5 minutes stirring occasionally. Poke the cake all over with the end of a wooden spoon. Pour warm pudding over warm cake. Tap the pan allowing the pudding to seep into the cake. Cover and refrigerate for 4 hours or overnight. (Frost after slightly cooled, about 30 minutes)
In a saucepan, combine milk, butter, & sugar over medium high heat. Bring to a rolling boil and allow to boil 45 seconds. Remove from heat and add chocolate chips. Whisk until smooth and shiny and immediately pour over the cake. Refrigerate until set.