Preheat the oven to 350 degrees. Lightly coat a 9x13 cake pan with cooking spray. Set aside.
In a medium mixing bowl combine flour, sugar, brown sugar, baking soda and salt. Whisk well. Set aside.
In a medium saucepan bring water and butter to a boil. As soon as the mixture boils, reduce heat to low and stir in 1/2 cup peanut butter and vegetable oil. When mixture is smooth, set aside and remove from heat.
In a large mixing bowl with electric mixer or a stand mixer fitted with a paddle attachment, combine 2 eggs, powdered buttermilk and water. Beat until smooth. Add hot peanut butter mixture from saucepan. Mix until cake batter is smooth.
Gradually add dry ingredients until fully combined. Batter will be light and slightly soupy. This is normal. Pour into greased cake pan.
Bake for 30 minutes or until top is a light golden brown and the center passes the toothpick test. Remove from the oven and frost immediately.
About 5 minutes before the cake is scheduled to be removed from the oven start to make the frosting. In a medium saucepan sugar,
evaporated milk and butter. Heat over medium-high, stirring continuously. When sugar is dissolved add creamy peanut butter, miniature marshmallows and vanilla. Stir until smooth and fully incorporated over very low heat.
Pour warm frosting mixture over hot Peanut Butter Cake and spread around to cover fully. Sprinkle with honey roasted peanuts immediately while frosting is still tacky.
Allow to cool completely before serving.
If you've tried this recipe, come back and let us know how it was!