Preheat the oven to 350 degrees F. Line a small baking dish with parchment paper or lightly spray with oil spray. Set aside.
In a bowl, mix the butter and sugar together until light and fluffy.
Mix in the egg and vanilla extract.
Add in the flour, baking powder and salt and stir until well blended.
Spread dough into prepared pan.
Bake in the preheated oven until lightly golden brown, 20-25 minutes.
Let cool completely in pan.