Combine flour, brown sugar, baking powder, baking soda, and salt. Break lumps with hands.

Stir in chocolate chips.

In small saucepan, melt butter and chocolate.

In separate small saucepan, heat vinegar and milk until barely warmed (no bubbling).

Remove chocolate and butter mixture from heat and stir in vanilla.

Pour mixture over dry ingredients. Add the milk mixture. Stir until combined.

Spread into greased 9×13 inch pan.

Combine brown sugar and cocoa in small bowl. Break chunks with hands. Sprinkle mixture evenly over cake batter.

Pour the boiling water evenly over the cake. (don't worry, it's supposed to look messy)

Carefully place in oven at 350 for 30 minutes.

Cool for 30 minutes.

Invert cake to serve so the fudge becomes a topping. Tastes great warm served with vanilla ice cream.