Creating this Peanut Butter Sheet Cake is easy if you follow these simple steps:

1. Preheat Oven: Preheat your oven to 350°F (175°C). Grease and flour a 13×18 inch sheet pan.
2. Mix Dry Ingredients: In a large bowl, whisk together the flour, baking powder, baking soda, and salt.
3. Cream Butter and Sugar: In another bowl, beat the softened butter and granulated sugar together until fluffy.
4. Add Peanut Butter: Mix in the peanut butter until well combined.
5. Incorporate Eggs and Milk: Add the eggs one at a time, mixing well after each addition. Then, stir in the milk and vanilla extract.
6. Combine Mixtures: Gradually add the dry ingredients to the wet mixture, stirring until just combined.
7. Pour Batter: Pour the batter into the prepared sheet pan and spread it evenly.
8. Bake: Place in the oven and bake for 25-30 minutes or until a toothpick inserted in the center comes out clean.
9. Cool the Cake: Remove from the oven and allow the cake to cool in the pan for about 20-30 minutes before transferring it to a wire rack to cool completely.
10. Prepare the Frosting: In a mixing bowl, beat together the peanut butter and softened butter. Gradually add the powdered sugar, milk, and vanilla extract, mixing until smooth.
11. Frost the Cake: Once the cake is completely cool, spread the peanut butter frosting evenly over the top.