Sheet Cake• 2 cups all-purpose flour (250g)• 1 cup granulated sugar (200g)• ¾ cups light brown sugar packed (150g)• ¾ teaspoon baking soda• ¾ teaspoon salt• 1 cup water (237ml)• ¾ cup unsalted butter (177g)• ¼ cup canola or vegetable oil (60g)• ½ cup creamy peanut butter (145g)• ½ cup buttermilk 118ml• 2 large eggs room temperature preferred• 1 ½ teaspoons vanilla extract
Pour batter evenly into prepared pan and transfer to center rack of 350F (175C) preheated oven and bake for 30-32 minutes or until a toothpick inserted in the center comes out clean.
Combine buttermilk, butter, peanut butter, and salt in a saucepan. Cook over low heat until butter is melted. Increase heat to medium and bring to a boil stirring constantly.