A rich and moist peanut butter sheet cake that is just as delicious as the standard Texas Sheet Cake!
Preheat oven to 375. Grease a large cookie sheet with sides (12x17 jellyroll sheet will work well).
In a saucepan, add peanut butter, water and butter and bring to a boil. Remove from heat.
In a separate bowl, mix sugar, brown sugar, flour, baking soda and salt. Stir well. Add to peanut butter mixture and stir until completely combined.
Add the eggs, vanilla and buttermilk. Mix well and pour into greased cookie sheet. Bake for 15 minutes until center springs back when touched.
While cake is cooking, in a small saucepan, bring butter, buttermilk and peanut butter to a boil. Remove from heat and add powdered sugar and vanilla. Whisk until completely combined.
When cake is removed from the oven, let sit for 3-5 minutes. Then pour frosting over still warm cake.