This easy and peanut buttery cake is perfect for feeding a crowd. It is made much like a Texas sheet cake and would be good with that chocolate icing, but we love it with white chocolate buttercream for an extra special treat!
In a large bowl, mix together flour, sugar, salt and baking soda.
In a small bowl, mix together milk and vinegar.
In a saucepan, melt butter over low heat. Stir in peanut butter until smooth and melted. Mix in hot water, bring to a bubble and remove from heat.
Mix the eggs and vanilla into the milk mixture.
Add hot peanut butter mixture to flour mixture and stir until just barely mixed. Stir in milk mixture and continue to stir until just incorporated.
Spread into a greased 13x18x1-inch half sheet pan and bake at 350°F for 25 minutes.
Icing
Add butter, milk, and peanut butter to a medium saucepan. Bring to a boil, while stirring.
Remove from heat and whisk in powdered sugar and vanilla.
Pour warm frosting over warm cake, using a spatula to spread it evenly. It should be thin enough to spread easily while it is warm. The frosting will set as it cools.