For the cake:
Cooking spray or butter
2 1/3 cups all-purpose flour
1 1/2 teaspoons baking powder
1 1/2 teaspoons baking soda
1/2 teaspoon salt
1 cup granulated sugar
1/2 cup vegetable oil
1/2 cup smooth peanut butter, at room temperature
3 large eggs
1 teaspoon vanilla extract
1 cup buttermilk or whole milk
For the PB&J swirl:
1/2 cup smooth peanut butter, at room temperature
1/3 cup powdered sugar
1 tablespoon vegetable oil
1/2 teaspoon vanilla extract
1/2 cup grape jelly
1 teaspoon hot water