1. Preheat the oven to 350°F and grease a 9×13 inch baking pan.
2. In a large bowl, combine flour, sugar, and baking soda. In a saucepan, melt 1 cup of butter. Stir in ½ cup cocoa powder and 1 cup buttermilk. Add this mixture to the dry ingredients.
3. Mix in eggs and 1 teaspoon vanilla extract. Pour batter into prepared pan and bake for 30-35 minutes.
4. For the frosting, beat together peanut butter, ½ cup butter, ¼ cup cocoa powder, ⅓ cup buttermilk, confectioners’ sugar, and 1 teaspoon vanilla extract. Spread over cooled cake.
5. For the fudge glaze, melt together 1 cup peanut butter, ½ cup butter, and ¼ cup cocoa powder. Pour over frosting. Let set before serving.