• Preheat oven to 350 F.  Grease and flour a 9X13" baking pan
• In a large mixing bowl, combine flour, sugar and baking soda with a whisk.  Set aside.
• Combine water, buttermilk and eggs in a medium bowl and whisk until slightly frothy.
• Melt butter in a medium saucepan over medium heat.  Stir in cocoa powder until combined.  Then add the buttermilk mixture.
• Cook the mixture over medium heat, stirring constantly, until just evenly boiling.
• Add this HOT mixture to the flour and beat until smooth - maybe 2 minutes or so. Add vanilla midway.
• Spread the batter into your prepared pan.
• Bake at 350 F for 35 minutes, or until a pick comes out clean.
• Remove from oven and cool in the pan on a wire rack for about 10 minutes.  Spread the peanut butter gently over the warm cake.  Then let it cool completely.
  

Fudge Icing

• Place the sugar in a large mixing bowl.  Melt the butter over medium heat (you can use the same pan you used before – less clean-up!)
• Add the buttermilk, then cocoa and stir constantly until mixture boils as before
• Pour the HOT mixture over the sugar and beat until smooth. It should reach an almost pourable consistency – if it turns dough-y, you’ll need a little bit more melted butter and buttermilk.
• Stir in vanilla.  Gently spread the icing over the peanut butter, then let the icing set for a while in a cool place (I covered mine with foil and put it in the fridge for about 30 minutes).

  Slice and serve.