Preheat your oven to 350°F (175°C) and line a cupcake tin with liners.
In a mixing bowl, combine the flour, sugar, baking powder, baking soda, and salt.
Add the peanut butter and softened butter to the dry ingredients and mix until well combined.
Beat in the eggs one at a time, then add the vanilla extract.
Gradually add the milk, mixing until the batter is smooth.
Divide the batter evenly among the cupcake liners.
Bake for 18-20 minutes or until a toothpick inserted into the center comes out clean.
Let the cupcakes cool in the tin for 5 minutes, then transfer to a wire rack to cool completely.