Preheat oven to 350°F and grease a 9×13-inch pan with butter or nonstick spray.

In a large bowl, whisk together flour, sugar, baking soda, and salt. Set aside.

In a large saucepan, bring butter and water to a boil. Remove from heat and whisk in peanut butter and oil until smooth.

Let cool 2 minutes, then whisk in eggs, milk, and vanilla until well mixed.

Add wet mixture to dry ingredients and mix until smooth. Pour batter into prepared pan and bake for 40-45 minutes until a toothpick inserted into the center comes out clean.

While the cake cools, make the frosting:

In a medium saucepan, bring butter, peanut butter, and milk to a rolling boil.

Remove from heat and stir in vanilla, then add powdered sugar gradually, whisking until smooth.

If needed, reheat slightly to ensure smooth consistency, then pour over the cake.

Quickly spread frosting evenly over the cake and top with roasted peanuts. Slice, serve, and enjoy!