🥜 Peanut Butter Sheet Cake 🎂
Ingredients
For the Cake
2 cups (250g) all-purpose flour
1 cup (200g) granulated sugar
¾ cup (150g) firmly packed light brown sugar
¾ teaspoon baking soda
¾ teaspoon salt
1 cup (237ml) water
¾ cup (177g) unsalted butter, cut into pieces
¼ cup (60ml) neutral oil (such as canola, vegetable, or avocado)
½ cup (145g) creamy peanut butter (not natural or oil-separated)
½ cup (118ml) buttermilk
2 large eggs, at room temperature
1½ teaspoons pure vanilla extract
For the Fudgy Peanut Butter Frosting
4 cups (500g) powdered sugar, sifted if lumpy
½ cup (118ml) buttermilk
10 tablespoons (150g) unsalted butter, cut into pieces
â…” cup (165g) creamy peanut butter (same as above)
¼ heaping teaspoon salt
1 teaspoon pure vanilla extract
Instructions
Prep & Preheat: Lightly grease a 13×9-inch baking pan. Preheat oven to 350°F (175°C).
Mix Dry Ingredients: In a large bowl, whisk together flour, granulated sugar, brown sugar, baking soda, and salt. Set aside.
Cook Wet Base: In a medium saucepan, combine water, butter, and oil. Heat over medium heat, stirring occasionally, until butter melts and mixture comes to a full boil. Remove from heat.
Incorporate Peanut Butter: Stir in ½ cup peanut butter until completely smooth. Pour this hot mixture into the dry ingredients and stir until combined. Let cool for 5–10 minutes.
Add Remaining Wet Ingredients: In a separate bowl, whisk buttermilk, eggs, and vanilla. Gradually stir this into the batter until just combined—do not overmix.
Bake the Cake: Pour batter evenly into the prepared pan. Bake on the center rack for 30–32 minutes, or until a toothpick inserted in the center comes out clean or with a few moist crumbs.
Make the Frosting: While the cake bakes, prepare the icing. In a clean saucepan, combine buttermilk, butter, â…” cup peanut butter, and salt. Cook over medium-low heat until butter melts, then increase to medium heat and bring to a gentle boil, stirring constantly. As soon as it boils, remove from heat.
Finish Frosting: Immediately whisk in sifted powdered sugar and vanilla until smooth and glossy. Work quickly—the mixture thickens as it cools.
Frost & Set: Pour the warm frosting directly over the hot cake (still in the pan). Use an offset spatula or the back of a spoon to spread evenly. Let cool completely before slicing—the icing will firm to a soft, fudgy texture.