Preheat oven to 350°F Grease and flour 2 9" round cake pans.
In a large bowl, cream the butter and pb until the mixture becomes fluffy. Mix in the brown sugar. Add the eggs, one at a time, mixing well after each addition.
In a small bowl, combine the flour, baking powder and salt. Add the flour mixture to the butter mixture along with the milk and blend. Add the vanilla.
Pour the batter into the prepared pans. Bake about 45 minutes, until a toothpick inserted in the center comes out clean. After the cake has cooled 5 minutes, place a covered cake board or cooling rack over the cake and turn over. Gently remove the pan from the cake. Allow to cool completely before frosting.
To make the PB filling, cream the cream cheese and pb together until fluffy.
Spread 3/4 cup of the PB filling over the top of each cake. Let chill in the fridge.
To make the chocolate glaze, combine the water and butter in a small saucepan. Bring toa boil. Add the cocoa, icing sugar and vanilla to the butter-water mixture. Mix until smooth.
Using a metal spatula dipped in hot water, spread half of the warm glaze over the pb topping on each cake. The glaze will thicken as it cools.