The Perfect Peanut Butter Sheet Cake
LOOKING FOR A DESSERT TO FEED A CROWD? THIS YUMMY PEANUT BUTTER SHEET CAKE WILL SERVE PLENTY! PERFECT FOR YOUR NEXT SUMMER BBQ, PICNIC, POT LUCK, OR FELLOWSHIP.
THIS DESSERT….. MMMMM.
The cake turns out moist and delicious and peanut buttery. And the frosting! Rich and even more peanut buttery. 🙂 It forms just a slight crustiness, making it simple to serve. No sticking to the plastic wrap or icing falling down the sides of each piece. I like to serve it on napkins and without silverware for a quick and easy end to a meal!
Certainly, a crowd favorite! Just take it to your next get together and you will find out!
Our S’mores Bars are also a crowd favorite!
By the way, if you are looking for a good sheet pan, I highly recommend the one that I have!
This commercial “half-sheet” by Nordic Ware is made from natural aluminum, which means it won’t rust. (I’ve used mine on a regular basis for years and don’t have even one spot of rust on it!)
I spray it with cooking spray and have never had a problem with anything sticking. So if you want a reliable one that will last, I recommend THIS ONE! 
Peanut Butter Sheet Cake
Ingredients
Cake
- 1/2 cup peanut butter
- 1 cup water
- 2 sticks margarine
- 2 cups flour
- 2 cups sugar
- 1 tsp salt
- 1 tsp baking soda
- 2 eggs
- 1/2 cup buttermilk
Frosting
- 1 stick margarine
- 1/2 cup peanut butter
- 6 Tbs buttermilk
- 1 tsp vanilla
- 4 cups powdered sugar
Instructions
- In bowl, mix together flour, sugar, salt and soda.
- In saucepan, mix together peanut butter, water and margarine.
- Bring to a rapid boil and pour over the flour mixture.
- Mix together and add the eggs and buttermilk.
- Pour into greased sheet cake pan. (or 2 - 9x13 pans) Bake at 350° for 20-25 min.
Frosting
- Bring margarine, peanut butter and buttermilk to a rapid boil.
- Remove from heat and add vanilla and powdered sugar.
- Frost cake while the frosting is still hot.
- Let cool completely and cut into bars.
If you’re looking for another dessert to feed a crowd, check out these crazy good S’mores Bars!!!
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Alicia O.
April 25, 2026I’ve made this cake multiple times, great went it turns out. But I find I usually have to remake the icing multiple times because trying to get the butter to melt the mixture breaks – becoming clumpy and oil. Does anyone else have this problem? And how to keep it from happening?
Rachel Barkowski
May 14, 2026Hi! Try melting the butter or margarine first – the peanut butter, butter or margarine, and buttermilk may look separated, but the powdered sugar will bring it all together. Be sure you’ve taken it off the heat before adding the vanilla and powdered sugar.