Preheat oven to 350º
Grease and flour a 9x13 baking dish and set aside.
In a large bowl combine dry ingredients (flour, sugar, cocoa, baking soda, baking powder and salt)
Add eggs, milk, oil and vanilla and beat on medium speed for 2 minutes, add coffee (or boiling water) and mix to combine (the batter will look runny). Pour it in the baking dish and smooth the top. Bake 35 to 40 minutes, (until toothpick inserted into center comes out clean). If the cake rises too much in the center and cracks, you can press it gently with your palms, when it's slightly cooled just to smooth the top.
With a wooden spoon poke holes all over the top of the cake and set aside.
Place chocolate chips in a heatproof bowl and set aside. In a saucepan bring sweetened condensed milk to a boil and pour it over chocolate chips. Whisk until smooth.
Pour chocolate mixture over the cake and spread to fill in the holes.
Set aside to cool (about an hour) then refrigerate until completely cooled.
To make the topping, mix heavy cream until soft peaks form, add powdered sugar, cocoa and vanilla extract and continue mixing until stiff peaks form. Spread it onto cooled cake and sprinkle with mini chocolate chips. Store in the fridge.