Old Fashioned Peanut Butter Cake

3.5 from 1164 votes

A good old fashioned peanut butter sheet cake with a crazy good warm frosting!

Prep Time25 mins

Cook Time40 mins

Total Time1 hr 5 mins

Course: Dessert

Cuisine: American

Servings: servings

Calories: 343kcal

2 cups all purpose flour
2 cups granulated sugar
1 tsp baking soda
1 tsp salt
1 stick, or 1/2 cup unsalted butter
1 cup water
1/2 cup creamy peanut butter Note: I used regular peanut butter for this recipe, 'natural'peanut butter does not work as well.
1/2 cup vegetable oil
2 large eggs room temperature
1/2 cup buttermilk room temperature
1 tsp vanilla extract

Preheat oven to 350F
Spray a 9x13 pan.
Whisk together the flour, sugar, baking soda, and salt and set aside.
Heat the butter and water in a medium/large saucepan until it comes to a boil. Take off the heat and whisk in the peanut butter and oil until smooth. Let cool for a few minutes, then whisk in the eggs, buttermilk, and vanilla until well blended.
Add the dry ingredients to the wet ingredients, and whisk until just combined.
Pour the batter into the prepared pan and bake for 40-45 minutes, until the top is golden and a toothpick inserted in the center comes out clean. Set the cake on a cooling rack while you make the frosting.
To make the frosting, put the butter, peanut butter, and buttermilk in a saucepan and bring to a full boil. Take off the heat and beat in the vanilla and powdered sugar, adding a cup at a time, until the frosting is smooth. I like to put it back on a gentle heat just to rewarm it, stirring constantly, before pouring over the cake. Note: if your frosting is very stiff and not pourable, add a little bit more buttermilk to thin it out.
Pour the hot frosting over the warm cake, working quickly because the frosting sets up immediately. Spread evenly over cake.
Garnish with peanuts.

Make it chunky! Yes, of course, go ahead and use chunky PB for this cake. I would still use smooth for the frosting, but that's your call.